Common Rail 2005

The Bosch Yellow Jackets Edition 2005

Exper Exp ertt Know-H Know-How ow on Autom Automoti otive ve Tec Techno hnolog logyy

Diesel Die sel-En -Engin gine e Manage Managemen mentt

Diesel Fuel-Injection Fuel-Injection System System Common-Rail

 Æ

• System System overview overview of passen passenger ger cars cars and commercial vehicles • Piezo Piezo-inli -inline ne injec injectors tors • High High-pre -pressur ssure e pump pumpss

Automotive Automot ive Technology Technology



Imprint

Published by:

© Robert Bosch GmbH, 2005 Postfach 11 1129, 29, D-73201 Plochingen. Automotive Aftermarket Business Sector, Department AA/PDT5. Product Marketing, Diagnostics & Test Equipment. Editorial team:

Dipl.-Ing. Karl-Heinz Dietsche, Dipl.-Phys. Maria Klingebiel, Dipl.-Ing. Ralf Müller. Authors:

Dipl.-Ing. Felix Landhäußer, Dr.-Ing. Ulrich Projahn, Dipl.-Inform. Michael Heinzelmann, Dr.-Ing. Ralf Wirth (Common-rail system), Ing. grad. Peter Schelhas, Dipl.-Ing. Klaus Ortner (Fuel-supply pumps), Dipl.-Betriebsw. Meike Keller (Fuel filters), Dipl.-Ing. Sandro Soccol, Dipl.-Ing. Werner Brühmann (High-pressure pumps), Ing. Herbert Strahberger Strahberger,, Ing. Helmut Sattmann (Fuel rail and add-on components), Dipl.-Ing. Thilo Klam, Dipl.-Ing. (FH) Andreas Rettich, Dr. techn. David Holzer, Dipl.-Ing. (FH) Andreas Koch (Solenoid-valve injectors), Dr.-Ing. Patrick Mattes (Piezo-inline injectors), Dipl.-Ing. Thomas Kügler (Injection nozzles), Dipl.-Ing. (FH) Mikel Lorente Susaeta, Dipl.-Ing. Martin Grosser, Dr.-Ing. Andreas Michalske (Electronic diesel control), Dr.-Ing. Günter Driedger, Dr. rer. nat. Walter Lehle, Dipl.-Ing. Wolfgang Schauer, Schauer, Rainer Heinzmann (Diagnostics) and the editorial team in co-operation with the responsible technical technical departments departments at Robertt Bosc Rober Bosch h GmbH. Unless otherwise indicated, the above are employees of Robert Bosch GmbH, Stuttgart.

Reproduction, duplication and translation of this publication, either in whole or in part, is permissible only with our prior written consent and provided the source is quoted. Illustrations, descriptions, schematic diagrams and the like are for explanatory purposes and illustration of the text only. They cannot be used as the basis for the design, installation, or specification of products. We accept no liability for the accuracy of the content of this document in respect of applicable statutory regulations. Robert Bosch GmbH is exempt from liability, Subject to alteration and amendment. Printed in Germany. Imprimé en Allemagne. 2nd edition, April 2005. English translation of the 3rd German edition dated: October 2004. (2.0)

Diesel Fuel-Injection System Common-Rail Robert Bosch GmbH



Contents

4 Overview of common-rail systems 4 Areas of application 5 Design 6 Operating concept 10 Common-rail system for passenger cars 15 Common-rail system for commercial vehicles 18 Fuel supply to the low-pressure stage 18 Overview 20 Fuel-supply pump 24 Fuel filter 26 High-pressure components of common-rail system 26 Overview 28 Injector 40 High-pressure pumps 46 Fuel rail (high-pressure accumulator) 47 High-pressure sensors 48 Pressure-control valve 49 Pressure-relief valve 50 Injection nozzles 52 Hole-type nozzles 56 Future development of the nozzle 58 High-pressure lines 58 High-pressure connection fittings 59 High-pressure delivery lines 62 Electronic Diesel Control (EDC) 62 System overview 64 Common-rail system for passenger cars 65 Common-rail system for commercial vehicles 66 Data processing 68 Fuel-injection control 76 Lambda closed-loop control for passenger-car diesel engines 81 Torque-controlled EDC systems 84 Data exchange with other systems 85 Serial data transmission (CAN)

86 Fault diagnostics 86 Monitoring during vehicle operation (On-board diagnosis) 89 On-board diagnostic system for passenger cars and light-duty trucks 90 Diagnostics in the workshop 92 Technical terms and acronyms 92 Technical terms 94 Acronyms Editorial boxes 9 Diesel boom in Europe 14 Overview of diesel fuel-injection systems 19 Electric fuel pump requirements 23 Diesel fuel filtration 27 Cleanliness requirements 38 The piezoelectric effect 39 Where does the word “electronics” come from? 51 Dimensions of diesel fuel-injection technology 57 High-precision technology 61 Cavitation in the high-pressure system 75 Injector delivery compensation 80 Closed-loop and open-loop control

Calls for lower fuel consumption, reduced exhaust-gas emissions, and quiet engines are making greater demands on the engine and fuel-injection system. These demands can only be met by a fuel-injection system that atomizes fuel at the nozzle finely enough and at a high injection pressure. At the same time the injected fuel quantity must be very  precisely metered, the rate-of-discharge curve must have an exact shape, and pre-injection and secondary injection must be performable. A system that meets these demands is the common-rail fuel-injection system. In contrast to other fuel-injection systems, fuel is supplied continuously to a high-pressure accumulator in readiness for injection. This edition in the Expert Know-How on Automotive Engineering series of booklets presents the design and operating concept of common-rail systems, and documents how this fuel-injection system has evolved since its market launch in 1997. It also describes in detail the main components of the common-rail system. The heart of the system is the injector, of which there are two types: the solenoid-valve injector and the new piezo-inline injector introduced 2004. This booklet will explain their operating concepts and the advantages of piezo technology. Another topic in this booklet is the description of Electronic Diesel Control (EDC). Only the electronics embedded in the common-rail system can exploit the opportunities of this fuel-injection system to the full. EDC is capable of meeting the diesel-engine demands listed above, as well as demands stipulated by emission-control legislation in future. Meanwhile, common rail has become the most commonly used fuel-injection system for modern, high-rev passenger car diesel engines.

4

Overview of common-rail systems

Areas of application

Overview of common-rail systems The demands placed on diesel-engine fuel-injection systems are continuously  increasing. Higher pressures, faster switching times, and a variable rate-of-discharge curve modified to the engine operating  state have made the diesel engine economical, clean, and powerful. As a result, diesel engines have even entered the realm of  luxury-performance sedans.

One of the advanced fuel-injection systems is the common-rail (CR) fuel-injection system. The main advantage of the commonrail system is its ability to vary injection pressure and timing over a broad scale. This was achieved by separating pressure generation (in the high-pressure pump) from the fuel-injection system (injectors). The rail here acts as a pressure accumulator.

1

Areas of application The common-rail fuel-injection system for engines with diesel direct injection (Direct Injection, DI) is used in the following vehicles:  Passenger cars ranging from high-economy 3-cylinder engines with displacements of 800 cc , power outputs of 30 kW (41 HP), torques of 100 Nm, and a fuel consumption of 3.5 l/100 km through to 8-cylinder engines in luxury-performance sedans with displacements of approx. 4 l , power outputs of 180 kW (245 HP), and torques of 560 Nm.  Light-duty trucks with engines producing up to 30 kW/cylinder, and  Heavy-duty trucks , railway locomotives , and ships with engines producing up to approx. 200 kW/cylinder

Common-rail fuel-injection system taking the example of a five-cylinder diesel engine

1

2 5 3

4 Fig. 1

1 Fuel return line 2 High-pressure fuel line to injector 3 Injector 4 Fuel rail 5 Rail-pressure sensor 6 High-pressure fuel line to rail 7 Fuel return line 8 High-pressure pump

7

6

8

     Y      1      9      9      1      K      M      U

     æ

Overview of common-rail systems

The common-rail system is a highly flexible system for adapting fuel injection to the engine. This is achieved by:  High injection pressure up to approx. 1,600 bar, in future up to 1,800 bar.  Injection pressure adapted to the operating status (200...1,800 bar).  Variable start of injection.  Possibility of several pre-injection events and secondary injection events (even highly retarded secondary injection events). In this way, the common-rail system helps to raise specific power output, lower fuel consumption, reduce noise emission, and decrease pollutant emission in diesel engines. Today common rail has become the most commonly used fuel-injection system for modern, high-rev passenger-car directinjection engines.

2

Areas of application, design

5

Design The common-rail system consists of the following main component groups (Figs. 1 and 2):  The low-pressure stage, comprising the fuel-supply system components.  The high-pressure system, comprising components such as the high-pressure pump, fuel rail, injectors, and high-pressure fuel lines.  The electronic diesel control (EDC), consisting of system modules, such as sensors, the electronic control unit, and actuators. The key components of the common-rail system are the injectors. They are fitted with a rapid-action valve (solenoid valve or piezo-triggered actuator) which opens and closes the nozzle. This permits control of the injection process for each cylinder.

System modules of an engine control unit and a common-rail fuel-injection system

Electronic diesel control (EDC): engine management, sensors, interface

Fuel supply system (low-pressure stage)

Air-intake and exhaust-gas systems

Engine

1 2 3

High-pressure section

Signals Diesel fuel

     E      1      7      8      1      K      M      N

     æ

Fig. 2

1 High-pressure pump 2 Fuel rail 3 Injectors

Overview of common-rail systems

6

Design, operating concept

All the injectors are fed by a common fuel rail, this being the origin of the term “common rail”. One of the main features of the commonrail system is that system pressure is variable dependent on the engine operating point. Pressure is adjusted by the pressure-control valve or the metering unit (Fig. 3). The modular design of the common-rail system simplifies modification of the system to different engines.

Fig. 3

a

Pressure control on the high-pressure side by means of pressure-control valve for passengercar applications b Pressure control on the suction side with a metering unit flanged to the highpressure pump (for passenger cars and commercial vehicles) c Pressure control on the suction side with a metering unit and additional control with a pressurecontrol valve (for passenger cars)

3

Examples of high-pressure control for common-rail systems

a 4

5 8

1 2

7

6

7

7

15 16 17 18 19 10 11

High-pressure pump Fuel inlet Fuel return Pressure-control valve Fuel rail Rail-pressure sensor Injector connection Return fuel connection Pressure-relief valve Metering unit Pressure-control valve

In the common-rail fuel-injection system, the functions of pressure generation and fuel injection are separate. The injection pressure is generated independent of the engine speed and the injected fuel quantity. The electronic diesel control (EDC) controls each of the components. Pressure generation Pressure generation and fuel injection are separated by means of an accumulator volume. Fuel under pressure is supplied to the accumulator volume of the common rail ready for injection. A continuously operating high-pressure pump driven by the engine produces the desired injection pressure. Pressure in the fuel rail is maintained irrespective of engine speed or injected fuel quantity. Owing to the almost uniform injection pattern, the highpressure pump design can be much smaller and its drive-system torque can be lower than conventional fuel-injection systems. This results in a much lower load on the pump drive.

The high-pressure pump is a radial-piston pump. On commercial vehicles, an in-line fuel-injection pump is sometimes fitted.

7

3

Pressure control The pressure control method applied is largely dependent on the system.

b 9

5

6

10

11 12 13 14

Operating concept

7

1 2

7

7

7

3

c 11 10 1 2

3

5 8

7

6

7

7

7      Y      3      9      9      1      K      M      S

     æ

Control on the high-pressure side On passenger-car systems, the required rail pressure is controlled on the high-pressure side by a pressure-control valve (Fig. 3a, 4). Fuel not required for injection flows back to the low-pressure circuit via the pressurecontrol valve. This type of control loop allows rail pressure to react rapidly to changes in operating point (e.g. in the event of load changes).

Overview of common-rail systems

Control on the high-pressure side was adopted on the first common-rail systems. The pressure-control valve is mounted preferably on the fuel rail. In some applications, however, it is mounted directly on the high-pressure pump. Fuel-delivery control on the suction side Another way of controlling rail pressure is to control fuel delivery on the suction side (Fig. 3b). The metering unit (10) flanged on the high-pressure pump makes sure that the pump delivers exactly the right quantity of  fuel to the fuel rail in order to maintain the injection pressure required by the system. In a fault situation, the pressure-relief valve (9) prevents rail pressure from exceeding a maximum. Fuel-delivery control on the suction side reduces the quantity of fuel under high pressure and lowers the power input of the pump. This has a positive impact on fuel consumption. At the same time, the temperature of the fuel flowing back to the fuel tank is reduced in contrast to the control method on the high-pressure side. Two-actuator system The two-actuator system (Fig. 3c) combines pressure control on the suction side via the metering unit and control on the high-pressure side via the pressure-control valve, thus marrying the advantages of high-pressureside control and suction-side fuel-delivery  control (see the section on “Common-rail system for passenger cars”). Fuel injection The injectors spray fuel directly into the engine’s combustion chambers. They are supplied by short high-pressure fuel lines connected to the fuel rail. The engine control unit controls the switching valve integrated in the injector to open and close the injector nozzle.

Operating concept

The injector opening times and system pressure determine the quantity of fuel delivered. At a constant pressure, the fuel quantity delivered is proportional to the switching time of the solenoid valve. This is, therefore, independent of engine or pump speed (time-based fuel injection). Potential hydraulic power Separating the functions of  pressure generation and fuel injection opens up further degrees of freedom in the combustion process compared with conventional fuel-injection systems; the injection pressure is more or less freely selectable within the program map. The maximum injection pressure at present is 1,600 bar; in future this will rise to 1,800 bar. The common-rail system allows a further reduction in exhaust-gas emissions by introducing pre-injection events or multiple in jection events and also attenuating combustion noise significantly. Multiple injection events of up to five per injection cycle can be generated by triggering the highly rapidaction switching valve several times. The nozzle-needle closing action is hydraulically  assisted to ensure that the end of injection is rapid.

7

8

Overview of common-rail systems

Operating concept

Control and regulation Operating concept The engine control unit detects the accelerator-pedal position and the current operating states of the engine and vehicle by means of  sensors (see the section on “Electronic diesel control”). The data collected includes:  Crankshaft speed and angle  Fuel-rail pressure  Charge-air pressure  Intake air, coolant temperature, and fuel temperature  Air-mass intake  Road speed, etc.

The electronic control unit evaluates the input signals. In sync with combustion, it calculates the triggering signals for the pressure-control valve or the metering unit, the injectors, and the other actuators (e.g. the EGR valve, exhaust-gas turbocharger actuators, etc.). The injector switching times, which need to be short, are achievable using the optimized high-pressure switching valves and a special control system. The angle/time system compares injection timing, based on data from the crankshaft and camshaft sensors, with the engine state (time control). The electronic diesel control (EDC) permits a precise metering of the in jected fuel quantity. In addition, EDC offers the potential for additional functions that can improve engine response and convenience. Basic functions The basic functions involve the precise control of diesel-fuel injection timing and fuel quantity at the reference pressure. In this way, they ensure that the diesel engine has low consumption and smooth running characteristics.

Correction functions for calculating fuel injection A number of correction functions are available to compensate for tolerances between the fuel-injection system and the engine (see the section on “Electronic diesel control”):  Injector delivery compensation  Zero delivery calibration  Fuel-balancing control  Average delivery adaption Additional functions Additional open- and closed-loop control functions perform the tasks of reducing exhaust-gas emissions and fuel consumption, or providing added safety and convenience. Some examples are:  Control of exhaust-gas recirculation  Boost-pressure control  Cruise control  Electronic immobilizer, etc. Integrating EDC in an overall vehicle system opens up a number of new opportunities, e.g. data exchange with transmission control or air-conditioning system. A diagnosis interface permits analysis of stored system data when the vehicle is serviced. Control unit configuration As the engine control unit normally has a maximum of only eight output stages for the injectors, engines with more than eight cylinders are fitted with two engine control units. They are coupled within the “master/slave” network via an internal, highspeed CAN interface. As a result, there is also a higher microcontroller processing capacity  available. Some functions are permanently  allocated to a specific control unit (e.g. fuelbalancing control). Others can be dynamically allocated to one or other of the control units as situations demand (e.g. to detect sensor signals).

Diesel boom in Europe



Diesel boom in Europe

Diesel engine applications At the start of automobile history, the sparkignition engine (Otto cycle) was the drive unit for road vehicles. The first time a diesel engine was mounted on a truck was 1927. Passenger cars had to wait until 1936. The diesel engine made strong headway in the truck sector due to its fuel economy and long service life. By contrast, the diesel engine in the car sector was long relegated to a fringe existence. It was only with the introduction of supercharged direct-injection diesel engines – the principle of direct injection was already used in the first truck diesel engines – that the diesel engine changed its image. Meanwhile, the percentage of diesel-engined passenger cars among new registrations is fast approaching 50% in Europe. Features of the diesel engine What is the reason for the boom in diesel engines in Europe? Fuel economy 

Firstly, fuel consumption compared to gasoline engines is still lower – this is due to the greater efficiency of the diesel engine. Secondly, diesel fuel is subject to lower taxes in most European countries. For people who travel a lot, therefore, diesel is the more economical alternative despite the higher purchase price. Driving pleasure

Almost all diesel engines on the market are supercharged. This produces a high cylinder charge at low revs. The metered fuel quantity can also be high, and this produces high engine torque. The result is a torque curve that permits driving at high torque and low revs.

It is torque, and not engine performance, that is the decisive factor for engine power. Compared to a gasoline engine without supercharging, a driver can experience more “driving pleasure” with a diesel engine of lower performance. The image of the “stinking slowcoach” is simply no longer true for dieselengined cars of the latest generation. Environmental compatibility 

The clouds of smoke that diesel-engined cars produced when driven at high loads are a thing of the past. This was brought about by improved fuel-injection systems and electronic diesel control (EDC). These systems can meter fuel quantity with high precision, adjusting it to the engine operating point and environmental conditions. This technology also meets prevailing exhaust-gas emission standards. Oxidation-type catalytic converters, that remove carbon monoxide (CO) and hydrocarbons (HC) from exhaust gas, are standard equipment on diesel engines. Future, more stringent exhaust-gas emission standards, and even U.S. legislation, will be met by other exhaust-gas treatment systems, such as particulate filters and NOx accumulator-type catalytic converters. 

Typical torque and power curves of a passenger-car diesel engine Nm

kW

360

100

320

90

280

 M 

80

    M

  e   u 240   q   r   o    T

 P

70

200

60

160

50

    P

  r   e   w   o    P

40 0

1,000 2,000 3,000 4,000 Engine speed

rpm

     E      3      2      0      2      K      M      S

     æ

9

10

Overview of common-rail systems

Common-rail system for passenger cars

Common-rail system for passenger cars Fuel supply In common-rail systems for passenger cars, electric fuel pumps or gear pumps are used to deliver fuel to the high-pressure pump.

Systems with electric fuel pump The electric fuel pump is either part of the in-tank unit (in the fuel tank) or is fitted in the fuel line (in-line). It intakes fuel via a pre-filter and delivers it to the high-pressure pump at a pressure of 6 bar (Fig. 3). The maximum delivery rate is 190 l /h. To ensure fast engine starting, the pump switches on as soon as the driver turns the ignition key. This builds up the necessary pressure in the low-pressure circuit when the engine starts. The fuel filter (fine filter) is fitted in the supply line to the high-pressure pump. Systems with gear pump The gear pump is flanged to the high-pressure pump and is driven by its input shaft (Figs. 1 and 2). In this way, the gear pump starts delivery only after the engine has started. Delivery rate is dependent on the engine speed and reaches rates up to 400 l /h at pressures up to 7 bar. A fuel pre-filter is fitted in the fuel tank. The fine filter is located in the supply line to the gear pump. Combination systems There are also applications where the two pump types are used. The electric fuel pump improves starting response, in particular for hot starts, since the delivery rate of the gear pump is lower when the fuel is hot, and therefore, thinner, and at low pump speeds.

High-pressure control On first-generation common-rail systems, rail pressure is controlled by the pressurecontrol valve. The high-pressure pump (type CP1) generates the maximum delivery  quantity, irrespective of fuel demand. The pressure-control valve returns excess fuel to the fuel tank. Second-generation common-rail systems control rail pressure on the low-pressure side by means of the metering unit (Figs. 1 and 2). The high-pressure pump (types CP3 and CP1H) need only deliver the fuel quantity that the engine actually requires. This lowers the energy demand of the high-pressure pump and reduces fuel consumption. Third-generation common-rail systems feature piezo-inline injectors (Fig. 3).

If pressure is only adjustable on the lowpressure side, it takes too long to lower the pressure in the fuel rail when rapid negative load changes occur. Adapting pressure to dynamic changes in load conditions is then too slow. This is particularly the case with piezo-inline injectors due to their very low  internal leakage. For this reason, some common-rail systems are equipped with an additional pressure-control valve (Fig. 3) besides the high-pressure pump and metering unit. This two-actuator system combines the advantages of control on the low-pressure side with the dynamic response of control on the high-pressure side. Another advantage compared with control on the low-pressure side only is that the high-pressure side is also controllable when the engine is cold. The high-pressure pump then delivers more fuel than is injected and pressure is controlled by the pressure-control valve. Compression heats the fuel, thus eliminating the need for an additional fuel heater.

Overview of common-rail systems

1

Common-rail system for passenger cars

11

Example of a second-generation common-rail system for a 4-cylinder engine Fig. 1 6 5

1

8

2 3

7

     Y      7      1      0      2      K      M      S

4

     æ

2

Example of a second-generation common-rail system with two-actuator system for a V8 engine

Fig. 2

5 8 1

6 9

5

2 3

7

     Y      8      1      0      2      K      M      S

4

3

1 High-pressure pump (CP3) with fitted geared presupply pump and metering unit 2 Fuel filter with water separator and heater (optional) 3 Fuel tank   4 Pre-filter 5 Fuel rail 6 Rail-pressure sensor 7 Solenoid-valve injector 8 Pressure-relief valve

     æ

1 High-pressure pump (CP3) with fitted geared presupply pump and metering unit 2 Fuel filter with water separator and heater (optional) 3 Fuel tank   4 Pre-filter 5 Fuel rail 6 Rail-pressure sensor 7 Solenoid-valve injector 8 Pressure-control valve 9 Function module (distributor)

Example of a third-generation common-rail system with two-actuator system for a 4-cylinder engine

Fig. 3 8

1

5

6

2 3

7

9 4

     Y      9      1      0      2      K      M      S

     æ

1 High-pressure pump (CP1H) with metering unit 2 Fuel filter with water separator and heater (optional) 3 Fuel tank   4 Pre-filter 5 Fuel rail 6 Rail-pressure sensor 7 Piezo-inline injector 8 Pressure-control valve 9 Electric fuel pump

12

Overview of common-rail systems

Common-rail system for passenger cars

System diagram for passenger cars Fig. 4 shows all the components in a common-rail system for a fully equipped, 4-cylinder, passenger-car diesel engine. Depending on the type of vehicle and its application, some of the components may  not be fitted.

The sensors and setpoint generators (A) are not depicted in their real installation position to simplify presentation. Exceptions are the exhaust-gas treatment sensors (F) and the rail-pressure sensor as their installation positions are required to understand the system.

Data exchange between the various sections takes place via the CAN bus in the “Interfaces” (B) section:  Starter motor  Alternator  Electronic immobilizer  Transmission control  Traction Control S  ystem (TSC)  Electronic Stability Program (ESP) The instrument cluster (13) and the air-conditioning system (14) are also connectable to the CAN bus. Two possible combined systems are described (a or b) for exhaust-gas treatment.

Fig. 4 Engine, engine management, and high-pressure

C

fuel-injection components

19 Fuel filter with overflow valve 20 Fuel tank with pre-filter and Electric Fuel Pump, EFP (presupply pump) 21 Fuel-level sensor

17 18 25 26 27 28 29 30 31 M

High-pressure pump Metering unit Engine ECU Fuel rail Rail-pressure sensor Pressure-control valve (DRV2) Injector Glow plug Diesel engine (DI) Torque

A

Sensors and setpoint generators

1 2 3 4 5 6 7 8 9 10 11 12

Pedal-travel sensor Clutch switch Brake contacts (2) Operator unit for vehicle-speed controller (cruise control) Glow-plug and starter switch (“ignition switch”) Road-speed sensor Crankshaft-speed sensor (inductive) Camshaft-speed sensor (inductive or Hall sensor) Engine-temperature sensor (in coolant circuit) Intake-air temperature sensor Boost-pressure sensor Hot-film air-mass meter (intake air)

B

Int erfaces

13 Instrument cluster with displays for fuel consumption, engine speed, etc. 14 Air-conditioner compressor with operator unit 15 Diagnosis interface 16 Glow control unit CAN Controller Area Network (on-board serial data bus)

D

Fuel-supply system (low-pressure stage)

Additive system

22 Additive metering unit 23 Additive control unit 24 Additive tank  E

Air supply

32 Exhaust-gas recirculation cooler 33 Boost-pressure actuator 34 Turbocharger (in this case with Variable Turbine Geometry (VTG)) 35 Control flap 36 Exhaust-gas recirculation actuator 37 Vacuum pump F

Exhaust-gas treatment

38 39 40 41 42 43 44

Broadband lambda oxygen sensor, type LSU Exhaust-gas temperature sensor Oxidation-type catalytic converter Particulate filter Differential-pressure sensor NOx accumulator-type catalytic converter Broadband lambda oxygen sensor, optional NOx sensor

Overview of common-rail systems

4

Common-rail system for passenger cars

Common-rail diesel fuel-injection system for cars

B

19

C

D

CAN

13

22

17 20

18 21

14

15

27

26

28

16

23

A

24

29 30

1

2

25

32 31

3

 M 

E 4 35 5

36

37

34 6

7

33

F

a 38

39

39

8 40

41

9 42 10

b 39

11

12

38

44

39

43

41

42

     Y      1         9      1      8      1      K      M      S

     æ

13

14

Overview of diesel fuel-injection systems



1

Overview of diesel fuel-injection systems

Areas of application

Requirements

Diesel engines are characterized by high fuel economy. Since the first volume-production fuel-injection pump was introduced by Bosch in 1927, fuel-injection systems have experienced a process of continuous development.

Ever stricter statutory regulations on noise and exhaust-gas emissions and the desire for more economical fuel consumption continually place greater demands on the fuel-injection system of a diesel engine.

Diesel engines are used in a wide variety of design for many different purposes (Fig. 1 and Table 1), for example  To drive mobile power generators (up to approx. 10 kW/cylinder)  As fast-running engines for cars and light-duty trucks (up to approx. 50 kW/cylinder)  As engines for construction-industry and agricultural machinery (up to approx. 50 kW/cylinder)  As engines for heavy trucks, omnibuses and tractor vehicles (up to approx. 80 kW/cylinder)  To drive fixed installations such as emergency power generators (up to approx. 160 kW/cylinder)  As engines for railway locomotives and ships (up to 1,000 kW/cylinder)

Basically, the fuel-injection system is required to inject a precisely metered amount of fuel at high pressure into the combustion chamber in such a way that it mixes effectively with the air in the cylinder as demanded by the type of engine (direct or indirect-injection) and its present operating status. The power output and speed of a diesel engine is controlled by means of the injected fuel quantity as it has no air intake throttle. Mechanical control of diesel fuel-injection systems is being increasingly replaced by Electronic Diesel Control (EDC) systems. All new diesel-injection systems for cars and commercial vehicles are electronically controlled.

Applications for Bosch diesel fuel-injection systems

M

M MW

PF

M MW

A/ P MW

P/H MW

ZWM CW

ZWM CW

PF

PF

PF

PF

PF

Fig. 1

M, MW, A, P, H, ZWM, CW In-line fuel-injection pumps of increasing size PF Discrete fuelinjection pumps VE Axial-piston pumps VR Radial-piston pumps UIS Unit injector system UPS Unit pump system CR Common-rail system

VE

VE

VE

VE

VE

VR

VR

VR

VR

VR

UIS

UIS

UIS

UIS

UIS

UPS

UPS

UPS PF(R)

UPS PF(R)

CR

CR

CR

CR

CR

CR

VE

     Y      4         3      6      5      1      K      M      U

     æ

Overview of common-rail systems

Common-rail system for commercial vehicles

Common-rail system for commercial vehicles

(Figs. 1 and 2). In many applications, it is mounted on the engine.

Fuel supply Presupply  Common-rail systems for light-duty trucks differ very little from passenger-car systems. Electric fuel pumps or gear pumps are used for fuel presupply. On common-rail systems for heavy-duty trucks, only gear pumps are used to deliver fuel to the high-pressure pump (see the subsection “Gear-type supply  pumps” in the section “Fuel supply in the low-pressure stage”). The presupply pump is normally flanged to the high-pressure pump

Fuel filtering As opposed to passenger-car systems, the fuel filter (fine filter) is fitted to the pressure side. For this reason, an exterior fuel inlet is required, in particular when the gear pump is flanged to the high-pressure pump.

1

15

Common-rail system for commercial vehicles with high-pressure pump (CP3)

7

8

9

5

Fig. 1

4

6

11 12 13 14

3

15 1      Y      5      2      0      2      K      M      S

10

2

     æ

2

16 17 18 19 10

Fuel tank  Pre-filter Fuel filter Gear presupply pump High-pressure pump (CP3.4) Metering unit Rail-pressure sensor Fuel rail Pressure-relief valve Injector

Common-rail system for commercial vehicles with high-pressure pump (CPN2)

7

6 5

8

Fig. 2

9

3

11 12 13 14

4

15 1 10

2

     Y      6      2      0      2      K      M      S

     æ

16 17 18 19 10

Fuel tank  Pre-filter Fuel filter Gear presupply pump High-pressure pump (CPN2.2) Metering unit Rail-pressure sensor Fuel rail Pressure-relief valve Injector

16

Overview of common-rail systems

Common-rail system for commercial vehicles

System diagram for commercial vehicles Fig. 3 shows all the components in a common-rail system for a 6-cylinder commercial-vehicle diesel engine. Depending on the type of vehicle and its application, some of  the components may not be fitted. Only the sensors and setpoint generators are depicted at their real position to simplify  presentation, as their installation positions are required to understand the system. Data exchange to the various sections takes place via the CAN bus in the “Interfaces” (B) section (e.g. transmission control,

Traction Control S ystem

Fig. 3

20 SCR control unit 21 Air compressor CAN Controller Area Network (on-board serial data bus) (up to three data buses)

Engine, engine management, and high-pressure fuel-injection components

22 29 30 31 32 33 34

High-pressure pump Engine ECU Fuel rail Rail-pressure sensor Injector Relay Auxiliary equipment (e.g. retarder, exhaust flap for engine brake, starter motor, fan) 35 Diesel engine (DI) 36 Flame glow plug (alternatively grid heater)  M  Torque A

Sensors and setpoint generators

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Pedal-travel sensor Clutch switch Brake contacts (2) Engine brake contact Parking brake contact Operating switch (e.g. vehicle-speed controller, intermediate-speed regulation, rpm- and torque reduction) Starter switch (“ignition lock”) Turbocharger-speed sensor Crankshaft-speed sensor (inductive) Camshaft-speed sensor Fuel-temperature sensor Engine-temperature sensor (in coolant circuit) Boost-air temperature sensor Boost-pressure sensor Fan-speed sensor Air-filter differential-pressure sensor

B

Interfaces

17 Air-conditioner compressor with operator unit 18 Alternator 19 Diagnosis interface

(TCS), Electronic Stability Program (ESP), oil-grade sensor, trip recorder, Active Cruise Control (ACC), brake coordinator – up to 30 ECUs). The alternator (18) and the air-conditioning system (17) are also connectable to the CAN bus. Three systems are described for exhaustgas treatment: a purely DPF system (a) mainly for the U.S. market, a purely SCR  system (b) mainly for the EU market, and a combined system (c).

C

Fuel-supply system (low-pressure stage)

23 24 25 26 27 28

Fuel presupply pump Fuel filter with water-level and pressure sensors Control unit cooler Fuel tank with pre-filter Pressure-relief valve Fuel-level sensor

D

Air intake

37 Exhaust-gas recirculation cooler 38 Control flap 39 Exhaust-gas recirculation positioner with exhaust-gas recirculation valve and position sensor 40 Intercooler with bypass for cold starting 41 Exhaust-gas turbocharger (in this case with variable turbine geometry) with position sensor 42 Boost-pressure actuator E

Exhaust-gas treatment

43 44 45 46 47 48 49 50 51 52 53 54

Exhaust-gas temperature sensor Oxidation-type catalytic converter Differential-pressure sensor Catalyst-coated particulate filter (CSF) Soot sensor Level sensor Reducing-agent tank  Reducing-agent pump Reducing-agent injector NOx sensor SCR catalytic converter NH3 sensor

Overview of common-rail systems

3

Common-rail system for commercial vehicles

Common-rail diesel fuel-injection system for commercial vehicles B

23

C

24

CAN

17

27

22

25 26

28 18

G

19

20

31

30

29

21

32

A

33

1

34

2 37

3

36

35

38

4

39

 M 

D 5 40

6 7

41 42

8

43

9

46

44

a

E

45

10 48

50

11 49 12 13

43 44

b

14

48

50 45

c

44

43

51

43 16

52 or 54

53

49

15

43

51

46

53

52 or 54 or 47

     Y      1         0      2      8      1      K      M      S

     æ

17

18

Fuel supply to the low-pressure stage

Overview

Fuel supply to the low-pressure stage The function of the fuel supply system is to store and filter the required fuel, and to provide the fuel-injection system with fuel at a specific supply pressure in all operating  conditions. For some applications, the return fuel is also cooled. In principle, the design of the fuel-supply  system is strongly dependent on the diesel injection system fitted. Fig. 1 shows the typical design of a common-rail system for passenger cars.

Overview The fuel-supply system comprises the following main components (Fig. 1):  Fuel tank   Pre-filter  Control unit cooler (optional)  Presupply pump (optional, also in-tank  pump on cars)  Fuel filter  Fuel pump (low-pressure)  Pressure-control valve (overflow valve)  Fuel cooler (optional)  Low-pressure fuel lines Fuel tank 

The fuel tank stores the fuel. It must be corrosion-resistant and leakproof at double the operating pressure, but at least at 0.3 bar. Any gage pressure must be relieved automatically by suitable vents or safety valves. When the vehicle is negotiating bends, inclines, or bumps, fuel must not escape past

1

Fuel system on a common-rail fuel-injection system

8 7 7

6

Fig. 1

11 12 13 14 15 16 17 18 19 10 11 12 13

Fuel tank  Pre-filter Presupply pump Fuel filter Low-pressure fuel lines High-pressure pump High-pressure fuel lines Fuel rail Injector Fuel return line Fuel-temperature sensor ECU Sheathed-element glow plug

10

9

11

10

12 13

5

EDC 16

4 5 1

3 2

     Y      9      0      0      2      K      M      U

     æ

Fuel supply to the l ow-pressure stage

the filler cap, or leak out of the pressurecompensation vents or valves.

Overview

Alternatively, an additional fuel pump can be provided as a presupply pump.

The fuel tank must be separated from the engine to prevent the fuel from igniting in case of an accident. Fuel lines

Besides metallic tubes, flexible, flame-retardant tubes reinforced with braided-steel armoring can be used in the low-pressure stage. The lines must be routed to avoid contact with moving components that could damage them, and to prevent leaking or evaporated fuel from collecting or igniting. The function of the fuel lines must not be impaired by the chassis twisting, the engine moving, or any other similar effects. All fuel-conveying parts must be protected against heat that may affect their proper operation. On buses, fuel lines may  not be routed though the passenger cabin or the driver’s cab. Fuel may not be gravity-fed. Diesel filter

Fuel-injection equipment for diesel engines are manufactured with great precision and are sensitive to the slightest contamination in the fuel. The fuel filter has the following functions:  Reduce particulate impurities to avoid particulate erosion.  Separate emulgated water from free water to avoid corrosion damage. The fuel filter must be adapted to the fuelinjection system. Fuel-supply pump

The fuel-supply pump draws fuel from the fuel tank and conveys it continuously to the high-pressure pump. The fuel pump is integrated in the high-pressure pump on axialpiston and radial-piston distributor pumps, and in a few instances in common-rail systems.



Electric fuel pump requirements

Electric Fuel Pumps (EFP) are increasingly

being fitted to passenger-car common-rail systems for fuel presupply. EFPs are mainly fitted inside of the fuel tank (in-tank pumps). Optionally, they can also be fitted to the supply line to the high-pressure pump (in-line pump). Compared with previous presupply pumps with mechanical drives, electric fuel pumps have distinct advantages in functions such as engine hot-start, first-start and restart response, as well as functional benefits at low fuel temperatures. The EFP in diesel applications differs from its gasoline counterpart in that a positive-displacement pump element and a coarser inlet strainer are fitted to replace the flow-type pump element. This is a rollercell pump element on Bosch systems. This system is highly robust, dirt-resistant, and particularly well-suited for use with diesel fuel. Firstly, the paraffins produced at low temperatures can still pass through the inlet strainer, and secondly, the higher level of contamination of diesel fuel does not damage the pump element. The in-tank pump is integrated in an in-tank unit. Other components of this unit include the fuel-level sensor, a suction-side fuel strainer, outlet protection valves, and a swirl plate acting as fuel reservoir. As opposed to gasoline systems, the fuel filter must be located outside of the fuel tank, as its function is also to separate water from the fuel and it must be accessible to change the filter.

19

20

Fuel supply to the low-pressure stage

Fuel-supply pump

automatically so that starting is possible even when the fuel tank has run dry.

Fuel-supply pump The fuel-supply pump in the low-pressure stage (the so-called presupply pump) is responsible for maintaining an adequate supply of fuel to the high-pressure components. This applies:  irrespective of operating state,  with a minimum of noise,  at the necessary pressure, and  throughout the vehicle’s complete service life. The fuel-supply pump draws fuel out of the fuel tank and conveys it continuously in the required quantity (injected fuel quantity and scavenging flow) to the high-pressure fuel-in jection installation (60...500 l /h, 300...700kPa or 3...7 bar). Many pumps bleed themselves

1

Single-stage electric fuel pump

1

6

C

2 B

Fig. 1

3

A Pumping element B Electric motor C End cover

4

1 2 3 4 5 6

Pressure side Motor armature Pumping element Pressure limiter Suction side Non-return valve

A

5

     Y      9         1      2      1      0      K      M      U

     æ

There are three designs:  Electric fuel pump (as used in passenger cars)  Mechanically driven gear-type supply  pumps, and  Tandem fuel pumps (passenger cars, UIS) In axial-piston and radial-piston distributor pumps, a vane-type supply pump is used as presupply pump and is integrated directly in the fuel-injection pump. Electric fuel pump The Electric Fuel Pump (EFP, Figs. 1 and 2)

is only fitted to passenger cars and lightduty trucks. As part of the system-monitoring strategy, it is responsible, besides fuel delivery, for cutting off the fuel supply, if this is necessary in an emergency. Electric fuel pumps are available as in-line or in-tank versions. In-line pumps are fitted to the vehicle’s body platform outside of the fuel tank in the fuel line between tank and fuel filter. On the other hand, in-tank pumps are located inside of the fuel tank in a special retainer that normally includes a suctionside fuel strainer, a fuel-level sensor, a swirl plate acting as fuel reservoir, and the electrical and hydraulic connections to the exterior. Starting with the engine cranking process, the electric fuel pump runs continuously, irrespective of engine speed. This means that it permanently delivers fuel from the fuel tank through a fuel filter to the fuelinjection system. Excess fuel flows back to the tank through an overflow valve. A safety circuit is provided to prevent the delivery of fuel if ignition is on and the engine is stopped. An electric fuel pump comprises three function elements inside of a common housing:

Fuel-supply pump

Fuel supply to the low-pressure stage

Pump element (Fig. 1, A) There are a variety of different pump-element designs available, depending on the electric fuel pump’s specific operating concept. Diesel applications mainly use roller-cell pumps (RCP). The roller-cell pump (Fig. 2) is a positivedisplacement pump consisting of an eccentrically located base plate (4) in which a slotted rotor (2) is free to rotate. There is a movable roller in each slot (3) which, when the rotor rotates, is forced outwards against the outside roller path and against the driving flanks of the slots by centrifugal force and the pressure of the fuel. The result is that the rollers now act as rotating seals, whereby a chamber is formed between the rollers of adjacent slots and the roller path. The pumping effect is due to the fact that, once the kidney-shaped inlet opening (1) has closed, the chamber volume reduces continuously. Electric motor (Fig. 1, B) The electric motor comprises a permanentmagnet system and an armature (2). Design is determined by the required delivery quantity at a given system pressure. The electric motor is permanently flushed by fuel so that it remains cool. This design permits high motor performance without the necessity 

2

for complicated sealing elements between pumping element and electric motor. End cover (Fig. 1, C) The end cover contains the electrical connections as well as the pressure-side hydraulic connection. A non-return valve (6) is incorporated to prevent the fuel lines from emptying once the fuel pump has been switched off. Interference suppressors can also be fitted in the end cover.

3

Specifications of a single-stage electric fuel pump

l/ h a 200   e    t   a   r

1

  y   r   e   v    i    l 100   e    D

2

3

4

5 6

Fig. 2

0 6

7

8

1 2 3 4 5

V

Voltage l/ h b   e    t 220   a   r   y   r   e   v    i    l   e    D160

9

Fig. 3

10

Parameter: delivery pressure a Delivery rate at low voltage b Delivery rate dependent on voltage in normal operation c Efficiency dependent on voltage

100 3

4

10

11

12

V

Voltage % c

7

1

5

     Y      4         0      2      1      0      K      M      U

     æ

  y   c   n   e    i   c    i    f    f    E

Suction (inlet) side Slotted rotor Roller Base plate Pressure side

7 8

Roller-cell pump (schematic)

2

21

8

28

9

26

10

24 10

11

12 Voltage

V

     E      8      0      0      2      K      M      U

     æ

11 12 13 14 15 16 17 18 19 10

at 200 kPa at 250 kPa at 300 kPa at 350 kPa at 400 kPa at 450 kPa at 450 kPa at 500 kPa at 550 kPa at 600 kPa

22

Fuel supply to the low-pressure stage

Fuel-supply pump

Gear-type fuel pump

Fig. 5

Pressure at pump outlet: 8 bar Parameter: suction-side pressure at pump inlet 1 500 mbar 2 600 mbar 3 700 mbar

Fig. 6

1 Suction side (fuel inlet) 2 Suction throttle 3 Primary gearwheel (drive wheel) 4 Secondary gearwheel 5 Pressure side

The gear-type supply pump (Figs. 4 and 6) is used to supply the fuel-injection modules of  single-cylinder pump systems (commercial vehicles) and common-rail systems (passenger cars, commercial vehicles, and off-road vehicles). It is directly attached to the engine or is integrated in the common-rail highpressure pump. Common forms of drive are via coupling, gearwheel, or toothed belt. The main components are two rotating, engaged gearwheels that convey the fuel in the tooth gaps from the suction side (Fig. 6, 1) to the pressure side (5). The line of contact between the rotating gearwheels provides the seal between the suction and pressure sides of the pump, and prevents fuel from flowing back again. The delivery quantity is approximately  proportional to engine speed, For this reason, fuel-delivery control takes place either by throttle control on the suction side, or by  means of an overflow valve on the pressure side (Fig. 5).

a hand pump can be installed directly on the gear pump, or in the low-pressure lines.

5

l /h

3

250

  y    t    i    t   n 200   a   u   q   y 150   r   e   v    i    l 100   e    D

2 1

50

0

6

1,000 2,000 3,000 Engine speed

rpm

     E      1      1      0      2      K      M      S

     æ

Fuel flow in the gear pump 5

3

The gear-type fuel pump is maintenancefree. In order to bleed the fuel system before the first start, or when the tank has run dry,

4

Delivery characteristics of the gear-type supply pump

4      Y      2      1      0      2      K      M      S

2

1

     æ

Exploded diagram of a gear pump 1

2

3

5

6

7

8

9

Fig. 4

1 2 3 4 5 6 7 8 9

Pump housing O-ring seal Primary gearwheel Secondary gearwheel Rivet C oupling Cover plate Molded seal Shaft seal

4

     Y      0      1      0      2      K      M      S

     æ

Electronic control unit



Diesel fuel filtration

Diesel fuel filtration

Special characteristics of diesel fuel

Compared to gasoline, diesel fuel has more impurities, and contains emulgated water, free water, and paraffin that can block the fuel filter in winter. Owing to these constituents in diesel, and the much higher injection pressures compared to gasoline fuel-injection systems, diesel fuel-injection systems require greater wear protection, extremely fine fuel filters, and measures to prevent blockage. Diesel fuel constituents

Impurities

Analyses of contaminated filter elements have shown that fuel can contain rust, water, organic substances (e.g.resins), fiber compounds, minerals (dust, sand), and abraded metals. These impurities may be entrained in the fuel, e.g. by incorrect fuel storage, via the fuel tank vent, or from the fuel tank itself (loose rust particles, etc.). The type of vehicle application is also important (e.g. operation on paved roads, offroad, or on construction sites). Hard foreign bodies cause the most wear if they migrate to critical points in the fuel-injection equipment. Organic aging substances or separated paraffin, which may occur if summer diesel is used in winter, is capable of blocking the filter material very rapidly. Water 

Diesel fuel may contain bound (emulgated) and unbound (free) water. Free water occurs as a result of condensate forming, e.g. through rapid changes in temperature. If water accesses the fuel-injection system, it may cause damage such as corrosion. Modern filter media separate water from the fuel completely. Firstly, water droplets collect in the pores on the soiled side of the filter element since fuel-flow pressure is insufficient to push them through the capillaries. More and more pores are then blocked by water deposits, preventing fuel from flowing through the filter. Pressure on the soiled side increases until the water is also pushed through the pores. On the clean side, water falls in droplets from the filter element and sinks to the bottom

of the water collection chamber due to the higher specific gravity of water compared to diesel fuel. From there, it can be drained. Paraffin

In the worst case, paraffin present in the diesel fuel starts to separate in the form of crystals at approx. 0°C or above. The paraffin crystals can block the fuel filter as temperature falls, thus cutting off the fuel supply. For this reason, diesel is subjected to a special treatment to make it suitable for winter operation. At the refinery, flow improvers are usually added to the fuel. Although this does not prevent paraffin from separating, it does inhibit the growth of crystals to a very great extent. The resulting crystals are so small that they pass very easily through the filter pores. Other additives maintain the small crystals in suspension, thus reducing the limits of filtration even further. European standard EN 590 defines a number of different categories of cold resistance. Diesel filters of the latest generation are fitted with electric fuel preheaters to prevent paraffin from blocking the filters in winter. This eliminates the need to add a small amount of gasoline or kerosine to the diesel fuel to improve its cold resistance. This somewhat controversial method was occasionally practised in the past, but is now prohibited. In some regions, filling stations offer diesel that permits troublefree operation down to –23°C.

23

24

Fuel supply to the low-pressure stage

Fuel filter

Fuel filter Design and requirements

Modern direct-injection (DI) systems for gasoline and diesel engines are highly sensitive to the smallest impurities in the fuel. Damage mainly occurs as a result of particulate erosion and water corrosion. The service-life design of the fuel-injection system depends on a specific minimum purity of  the fuel. Particulate filtration Reducing particulate impurities is one of  the functions of the fuel filter. In this way, it protects the wear-prone components of  the fuel-injection system. In other words, the fuel-injection system prescribes the necessary filter fineness. Besides wear protection, fuel filters must also have a sufficient particulate storage capacity, otherwise they  could become blocked before the end of the change interval. If they do become blocked, they would reduce fuel delivery quantity as well as engine performance. It is therefore essential to fit a fuel filter tailored to the requirements of the fuel-injection system. Fitting the incorrect filters would have unpleasant results at best; at worst, it would have very expensive consequences (from replacing components through to renewing the complete fuel-injection system). Compared to gasoline fuel, diesel fuel contains many more impurities. For this reason, and also due to the much higher injection pressures, diesel fuel-injection systems require greater wear protection, larger filtration capacities, and longer service lives. As a result, diesel filters are designed as exchange filters. Requirements regarding filter fineness have increased dramatically in the last few   years with the introduction of second-generation common-rail systems and further advances in Unit Injector Systems for passenger cars and commercial vehicles. Depending on the application (operating conditions, fuel contamination, engine life), new systems require filtration efficiencies

ranging from 65% to 98.6% (particle size 3 to 5 µm, ISO/TR 13353:1994). Longer servicing intervals in more recent vehicles require greater particulate storage capacities as well as intensive fine particulate filtration. Water separation The second main function of diesel fuel filters is to separate emulgated and undissolved water from the fuel in order to avoid corrosion damage. Efficient water separation greater than 93% at maximum flow (ISO 4020:2001) is a specially important factor for distributor injection pumps and common-rail systems. Designs

The filter must be carefully selected depending on the fuel-injection system and the operating conditions. Main filter The diesel fuel filter is normally fitted in the low-pressure circuit between the electric fuel pump and the high-pressure pump in the engine compartment.

1

Diesel exchange filter with spiral vee-shaped filter element

     Y      0      2      0      2      K      M      U

     æ

Fuel supply to the low-pressure stage

The use of screw-on exchange filters, in-line filters, and metalfree filter elements is widespread. The replacement parts are inserted in filter housings made of aluminum, solid plastic, or sheet steel (to meet higher crash requirements). Only the filter element is replaced in these filters. The filter elements are mainly spiral vee-shaped (Fig. 1). Two filters can also be fitted in parallel, resulting in greater particulate storage capacity. Connecting the filter in series produces a higher filtration efficiency. Stepped filters, or a fine filter with a matched prefilter, are used in series connections. Pre-filter for presupply pump If requirements are particularly high, an additional pre-filter is fitted on the suction or pressure side with a filter fineness matched to the main filter (fine filter). Pre-filters are mainly used for commercial vehicles in countries that have poor diesel fuel quality. These filters are mainly designed as strainers with a mesh width of 300 µm.

2

Diesel fuel filter with water drain and water sensor

Fuel filter

Water separator Water is separated by the filter medium using the repellent effect (droplets forming due to the different surface tensions of water and fuel). Separated water collects in the chamber at the bottom of the filter housings (Fig. 2). Conductivity sensors are used in some cases to monitor the water level. The water is drained manually by opening a water drain plug or pressing a pushbutton switch. Fully automatic water-disposal systems are currently under development. Filter media

Increased demands with respect to fuel filters in engines of the new generation require the use of special filter media composed of  several synthetic layers and cellulose. The filter media employ a preliminary fine filtering effect and guarantee maximum particulate retention capacity by separating particles within each filtering layer. The new filter generation is also deployable with biodiesel (Fatty Acid Methyl Ester (FAME). However, the higher concentration of organic particles in FAME means taking account of a shorter filter service life in the servicing concept. Additional functions

Modern filter modules integrate additional modular functions such as:  Fuel preheating: Electrically, by cooling water, or by return fuel flow. Preheating prevents paraffin crystals from blocking the filter pores in winter.  Displaying the servicing interval by  measuring differential pressure.  Filling and venting facilities: After a filter change, the fuel system is filled and vented by hand pump. The pump is usually integrated in the filter cover.      Y      1      2      0      2      K      M      U

     æ

25

26

Overview

High-pressure components of common-rail system

High-pressure components of common-rail system The high-pressure stage of the common-rail system is divided into three sections: pressure generation, pressure storage, and fuel metering. The high-pressure pump assumes the function of pressure generation. Pressure storage takes place in the fuel rail to  which the rail-pressure sensor and the pressure-control and pressure-relief valves are fitted. The function of the injectors is correct timing and metering the quantity of  1

fuel injected. High-pressure fuel lines interconnect the three sections.

Overview The main difference in the various generations of common-rail systems lie in the design of the high-pressure pump and the in jectors, and in the system functions required (Table 1).

Overview of common-rail systems

CR generation

Maximum pressure Injector

High-pressure pump

1st generation

1,350...1,450 bar

CP1

Solenoid-valve injector

Pass. cars

Pressure control on high-pressure side by pressurecontrol valve

1st generation

1,400 bar

Solenoid-valve injector

Comm. veh. 2nd generation

CP2 Suction-side fuel-delivery control by two solenoid valves

1,600 bar

Solenoid-valve injector

Pass. cars and

CP3, CP1H Suction-side fuel-delivery control by metering unit

comm. veh.

Table 1

3rd generation Pass. cars

1,600 bar (in future 1,800 bar)

Piezo-inline injector

CP3, CP1H Suction-side fuel-delivery control by metering unit

3rd generation Comm. veh.

1,800 bar

Solenoid-valve injector

CP3.3NH Metering unit

1

Common-rail fuel-injection system taking the example of a four-cylinder diesel engine 1

2

3

Fig. 1

1 2 3 4

5 6 7 8 9

Hot-film air-mass meter Engine EC U High-pressure pump High-pressure accumulator (fuel rail) Injector Crankshaft-speed sensor Engine-temperature sensor Fuel filter Pedal-travel sensor

4

5

6

7

8

9

     Y      1         6      6      5      1      K      M      U

     æ

Electronic control unit



Cleanliness requirements

Cleanliness requirements

Cleanliness quality The sharp rise in the performance of new assemblies, e.g.the common-rail system for high-pressure diesel fuel injection, requires extreme precision in machining, and ever tighter tolerances and fits. Particle residue from the production process may lead to increased wear, or even the total failure of the assembly. This results in high requirements and tight tolerances for cleanliness quality, with a continuous reduction in the permitted particle size. The cleanliness quality of components is currently determined in the production process by light-microscope image-analysis systems. They supply information on particlesize distribution. Additional information, such as the nature of the particles and their chemical composition, is required to develop innovative cleaning processes. This information is obtained by electron microscopes. Particle-analysis system (SEM) Bosch uses a particle-analysis system based on a Scanning Electron Microscope (SEM). This system performs an automated analysis of particles adhering to a product. The results of the analysis show particle-size distribution, the chemical composition of the particles, and images of the individual particles. Using this information, the source of the particles are identifiable. Action can then be taken to avoid, reduce, or wash off certain particle types. In this way, solutions are not based on the increased use of cleaning techniques, but on avoiding and reducing residual soiling during the production process. The automated particle-analysis system (SEM) provides the cleanliness process with an analysis system that produces important information on the type of residual soiling. The precise identification of particles and their sources is vital to developing new cleaning techniques.



Principle of the particle-analysis system (SEM)

Evolution of particulate-analysis process Particulate Microparticles up to < 1µm Light microscope

Electron microscope

Growth in information content - Number of particles - Size distribution

- EDX analysis - Number of particles - Size distribution - High precision (focus depth)

The electron beam and its action

Backscatter electrons and X-rays from depth of several m

Heat

Secondary electrons from depth of several m

Primary electron beam 20 kV Backscatter electrons to BSE detector (up to 20 keV) Secondary electrons to SE detector (several eV) X-rays to EDX detector (up to 10 keV)

Detection of interaction between electron beam and sample Secondary electrons of sample surface are converted into image signals. - Plastic image of surface (REM images). Backscatter electrons are converted into image signals. Phase composition TOPO mode plastic image Characteristic X-ray is converted into "energy-dispersive" spectrum. Identification of chemical elements

      E       9       6       1       0       N       A       S

     æ

27

28

High-pressure components of common-rail system

Injector

Injector On a common-rail diesel injection system, the injectors are connected to the fuel rail by  short high-pressure fuel lines. The injectors are sealed to the combustion chamber by a copper gasket. The injectors are fitted into the cylinder head by means of taper locks. Depending on the injection-nozzle design, common-rail injectors are intended for straight or inclined mounting in directinjection diesel engines. One of the system’s features is that it generates an injection pressure irrespective of  engine speed or injected fuel quantity. The start of injection and injected fuel quantity  are controlled by the electrically triggered injector. The injection time is controlled by the angle/time system of the Electronic Diesel Control (EDC). This requires the use 1

a b c

Resting position Injector opens Injector closes

11 12 13 14 15 16

Fuel-return Solenoid coil Overstroke spring Solenoid armature Valve ball Valve-control chamber Nozzle spring Pressure shoulder of nozzle needle Chamber volume Injection orifice Solenoid-valve spring Outlet restrictor High-pressure connection Inlet restrictor Valve plunger (control plunger) Nozzle needle

17 18 19 10 11 12 13 14 15 16

There are presently three different injector types in serial production:  Solenoid-valve injectors with one-part armature  Solenoid-valve injectors with two-part armature  Injector with piezo actuator

Solenoid-valve injector (functional schematic)

a

Fig. 1

of sensors to detect the crankshaft position and the camshaft position (phase detection). An optimum mixture formation is required to reduce exhaust-gas emissions and comply with continuous demands to reduce the noise of diesel engines. This calls for in jectors with very small pre-injection quantities and multiple injection events.

b

c

1

2

3

11

12

4 5

13

6 14 7

15

8

9 16 10

     Y      1         5      5      8      1      K      M      U

     æ

High-pressure components of common-rail system

Solenoid-valve injector

Design The injector can be subdivided into a number of function modules:  The hole-type nozzle (see the section on “Injection nozzle”)  The hydraulic servo system  The solenoid valve Fuel is conveyed by the high-pressure connection (Fig. 1a, 13) via a supply passage to the injection nozzle and via an inlet restrictor (14) to the valve-control chamber (6). The valve-control chamber is connected to the fuel return (1) via the outlet restrictor (12) which can be opened by a solenoid valve. Operating concept The function of the injector can be subdivided into four operating states when the engine and the high-pressure pump are operating:  Injector closed (with high pressure applied)  Injector opens (start of injection)  Injector fully open  Injector closes (end of injection) The operating states are caused by the balance of forces acting on the injector components. When the engine is not running and the fuel rail is not pressurized, the nozzle spring closes the injector. Injector closed (resting position) In its resting position, the injector is not triggered (Fig. 1a). The solenoid-valve spring (11) presses the valve ball (5) onto the seat of the outlet restrictor (12). Inside of the valve-control chamber, the pressure rises to the pressure in the fuel rail. The same pressure is also applied to the chamber volume (9) of the nozzle. The forces applied by the rail pressure to the end faces of the control plunger (15), and the force of the nozzle spring (7) retain the nozzle needle closed against the opening force applied to its pressure shoulders (8).

Injector

Injector opens (start of injection) To begin with, the injector is in its resting position. The solenoid valve is triggered by  the “pickup current”. This makes the solenoid valve open very rapidly (Fig. 1b). The required rapid switching times are achieved by controlling solenoid-valve triggering in the ECU at high voltages and currents. The magnetic force of the now triggered electromagnet exceeds the force of the valve spring. The armature raises the valve ball from the valve seat and opens the outlet restrictor. After a short time the increased pickup current is reduced to a lower holding current in the electromagnet. When the outlet restrictor opens, fuel flows from the valve-control chamber to the cavity above and then via the fuel-return line to the fuel tank. The inlet restrictor (14) prevents a complete pressure compensation. As a result, pressure in the valve-control chamber drops. Pressure in the valve-control chamber falls below the pressure in the nozzle chamber, which is still the same as the pressure in the fuel rail. The reduction in pressure in the valve-control chamber reduces the force acting on the control plunger and opens the nozzle needle. Fuel injection commences. Injector fully open  The rate of movement of the nozzle needle is determined by the difference in the flow  rates through the inlet and outlet restrictors. The control plunger reaches its upper stop and dwells there on a cushion of fuel (hydraulic stop). The cushion is created by the flow of fuel between the inlet and outlet restrictors. The injector nozzle is then fully  open. Fuel is injected into the combustion chamber at a pressure approaching that in the fuel rail. The balance of forces in the injector is similar to that during the opening phase. At a given system pressure, the fuel quantity  injected is proportional to the length of time that the solenoid valve is open. This is entirely independent of the engine or pump speed (time-based injection system).

29

30

High-pressure components of common-rail system

Injector

Injector closes (end of injection) When the solenoid valve is no longer triggered, the valve spring presses the armature down and the valve ball closes the outlet restrictor (Fig. 1c). When the outlet restrictor closes, pressure in the control chamber rises again to that in the fuel rail via the inlet restrictor. The higher pressure exerts a greater force on the control plunger. The force on the valve-control chamber and the nozzlespring force then exceed the force acting on the nozzle needle, and the nozzle needle closes. The flow rate of the inlet restrictor determines the closing speed of the nozzle needle. The fuel-injection cycle comes to an end when the nozzle needle is resting against its seat, thus closing off the injection orifices.

Another feature of the fuel-quantity map is the flat curve that occurs with small triggering periods. The flat curve is caused by the solenoid armature rebounding on opening. In this section, the injected fuel quantity is independent on the triggering period. This allows small injected fuel quantities to be represented as stable. Only after the armature has stopped rebounding does the injected fuel quantity curve continue to rise linearly  as the triggering period becomes longer. Injection events with small injected fuel quantities (short triggering periods) are used as pre-injection in order to suppress noise. Secondary injection events help to enhance soot oxidation in selected sections of the operating curve.

This indirect method is used to trigger the nozzle needle by means of a hydraulic servo system because the forces required to open the nozzle needle rapidly cannot be generated directly by the solenoid valve. The “control volume”required in addition to the injected fuel quantity reaches the fuel-return line via the restrictors in the control chamber. In addition to the control volume, there are also leakage volumes through the nozzleneedle and valve-plunger guides. The control and leakage volumes are returned to the fuel tank via the fuel-return line and a collective line that comprises an overflow valve, high-pressure pump, and pressure-control valve.

Program maps without fuel-quantity flat curve  The increasing stringency of emission-control legislation has lead to the use of the two system functions: injector delivery compensation (IMA) and zero delivery calibration  (NMK), as well as to short intervals in injection between pre-injection, main injection, and secondary injection events. With injectors that have no flat-curve section, IMA allows a precise adjustment of the pre-injection fuel quantity when new. NMK corrects fuel-quantity drifts over time in the lowpressure section. The key condition for deploying these two system functions is a constant, linear rise in quantity, i.e. there is no flat curve in the fuel-quantity map (Fig. 2c). If the valve plunger/nozzle needle unit is operated in nominal mode without lift-stop at the same time, this represents a fully ballistic operating mode of the valve plunger and there is no kink in the fuel-quantity map.

Program-map variants Program maps with fuel-quantity flat curve  With injectors, a distinction is made in the program map between ballistic and nonballistic modes. The valve plunger/nozzle needle unit reaches the hydraulic stop if the triggering period in vehicle operation is of  sufficient length (Fig. 2a). The section until the nozzle needle reaches its maximum stroke is termed ballistic mode. The ballistic and nonballistic sections in the fuel-quantity  map, where the injected fuel quantity is applied for the triggering period (Fig. 2b), is separated by a kink in the program map.

Injector variants A distinction is made between two different solenoid-valve concepts with solenoid-valve injectors:  Injectors with one-part armature (1-spring system)  Injectors with two-part armature (2-spring system)

High-pressure components of common-rail system

The short intervals between injection events are ensured when the armature can return to its resting position very rapidly on closing. This is best achieved by a two-part armature with an overstroke stop. During the closing process, the armature plate moves down by  positive locking. The bottoming-out of the armature plate is limited by an overstroke stop. As a result, the armature reaches its resting position faster. Armature rebound

2

Injector

on closing can end faster by decoupling the armature masses and adapting the setting parameters. This helps to achieve shorter intervals between two injection events with the two-part armature concept.

Needle lift and fuel-quantity maps of an injector with lift-stop

a

Valve plunger/nozzle needle unit at hydraulic stop Nonballistic section    t    f    i    l   e    l    d   e   e    N

Ballistic section Accumulation due to rail pressure

Time t  b

  y    t    i    t   n   e   a   g   u   n   q   e    l   m   e   z   u    t    f    i     r    d   p   s   e    t   n    i   c   e    E    j   n    I

Flat curve Nonballistic section

  e   r   u   s   s   e   r   p    l    i   a    R

Ballistic section

c

  y    t    i    t   e   n   g   a   n   u   e   q    l   m   e   z    t    i   u    f   r     p    d   s   e   n    t    i   c    E   e    j   n    I

  e   r   u   s   s   e   r   p    l    i   a    R

Full ballistic section without lift-stop

Triggering period

     E      3      8      9      1      K      M      U

     æ

31

32

High-pressure components of common-rail system

Injector

Triggering the solenoid-valve injector In its resting position, the injector’s highpressure solenoid valve is not triggered and is therefore closed. The injector injects when the solenoid valve opens. Triggering the solenoid valve is divided into five phases (Figs. 3 and 4). Opening phase  Initially, in order to ensure tight tolerances and high levels of reproducibility for the in jected fuel quantity, the current for opening the solenoid valve features a steep, precisely  defined flank and increases rapidly up to approx. 20 A. This is achieved by means of a booster voltage of up to 50V. It is generated in the control unit and stored in a capacitor (booster-voltage capacitor). When this voltage is applied across the solenoid valve, the current increases several times faster than it does when only battery voltage is used.

Holding-current phase  In order to reduce power loss in the ECU and injector, the current is dropped to approx. 13 A in the holding-current phase. The energy which becomes available when pickup current and holding current are reduced is routed to the booster-voltage capacitor. Switchoff  When the current is switched off in order to close the solenoid valve, the surplus energy is also routed to the booster-voltage capacitor. Recharging the step-up chopper  Recharging takes place by means of a stepup chopper integrated in the ECU. The energy tapped during the opening phase is recharged at the start of the pickup phase until the original voltage required to open the solenoid valve is reached.

Pickup-current phase  During the pickup-current phase, battery  voltage is applied to the solenoid valve and assists in opening it quickly. Current control limits pickup current to approx. 20 A. 3

Triggering sequence of a high-pressure solenoid valve for a single injection event

a

b

c

d

e

Solenoid-valve current I M

Solenoid-valve needle lift hM Fig. 3

a b c d e

Opening phase Pickup-current phase Transition to holdingcurrent phase Holding-current phase Switchoff

Injected fuel quantity Q

Time  t 

     E      1         3      4      7      0      E      A      S

     æ

Injector

High-pressure components of common-rail system

4

33

Common-rail system: Block diagram of the triggering phases for a cylinder group

2

4

 I 

a Opening phase 3

3

 I 

6

1  I 

7

5

6

7

 I 

b Pickup-current phase

 I 

 I 

c Transition to holding-current phase

 I 

 I 

 I 

d Holding-current phase

 I 

 I 

Fig. 4

e Switchoff  I 

f Recharging the step-up chopper

DC/DC converter: recharging the energy accumulator (9) 9 1

Energy transfer (from 9 to 5)

10 5

8

 I 

     E      1         7      5      7      1      K      M      S

     æ

11 Battery 12 Current control 13 Solenoid windings of the high-pressure solenoid valves 14 Booster switch 15 Booster-voltage capacitor 16 Free-wheeling diodes for energy recovery and highspeed quenching 17 Cylinder selector switch 18 DC/DC switch 19 DC/DC coil 10 DC/DC diode  I  Current flow

34

Injector

High-pressure components of common-rail system

Piezo-inline injector

Design and requirements The design of the piezo-inline injector is divided into its main modules in the schematic (see Fig. 5):  Actuator module (3)  Hydraulic coupler or translator (4)  Control or servo valve (5)  Nozzle module (6) The design of the injector took account of  the high overall rigidity required within the actuator chain composed of actuator, hydraulic coupler, and control valve. Another design feature is the avoidance of mechani5

Construction of the piezo-inline injector

1

2

3

Operating concept Function of the 3/2-way servo valve in the CR injector  The nozzle needle on piezo-inline injector is controlled indirectly by a servo valve. The required injected fuel quantity is then controlled by the valve triggering period. In its non-triggered state, the actuator is in the starting position and the servo valve is closed (Fig. 6a), i.e. the high-pressure section is separated from the low-pressure section.

4

Fig. 5

1 2 3 4 5 6 7

Fuel return High-pressure connection Piezo actuator module Hydraulic coupler (translator) Ser vo valve (control valve) Nozzle module with nozzle needle Injection orifice

5

6

7

cal forces acting on the nozzle needle. Such forces occurred as a result of the push rod used on previous solenoid-valve injectors. On aggregate, this design effectively reduces the moving masses and friction, thus enhancing injector stability and drift compared to conventional systems. In addition, the fuel-injection system allows the implementation of very short intervals (“hydraulic zero”) between injection events. The number and configuration of  fuel-metering operations can represent up to five injection events per injection cycle in order to adapt the requirements to the engine operating points. A direct response of the needle to actuator operation is achieved by coupling the servo valve (5) to the nozzle needle. The delay  between the electric start of triggering and hydraulic response of the nozzle needle is about 150 microseconds. This meets the contradictory requirements of high needle speeds and extremely small reproducible injected fuel quantities. As a result of this principle, the injector also includes small direct leakage points from the high-pressure section to the low-pressure circuit. The result is an increase in the hydraulic efficiency of the overall system.

     Y      1         4      7      9      1      K      M      U

     æ

High-pressure components of common-rail system

The nozzle is kept closed by the rail pressure exerted in the control chamber (3). When the piezo actuator is triggered, the servo valve opens and closes the bypass passage (Fig. 6b). The flow-rate ratio between the outlet restrictor (2) and the inlet restrictor (4) lowers pressure in the control chamber and the nozzle (5) opens. The control volume flows via the servo valve to the lowpressure circuit of the overall system. To start the closing process, the actuator is discharged and the servo valve releases the bypass passage. The control chamber is then refilled by reversing the inlet and outlet restrictors, and pressure in the control chamber is raised. As soon as the required pressure is attained, the nozzle needle starts to move and the injection process ends. The valve design described above and the greater dynamic design of the actuator system result in much shorter injection times compared to injectors of conventional design, i.e. push rod and 2/2-way valve. Ultimately, this has a positive impact on exhaust-gas emissions and engine performance. Due to requirements regarding the engine in EU 4, the injector program maps were optimized to apply corrective functions (injector delivery compensation (IMA) and 6

Injector

35

zero delivery calibration (NMK). The preinjection quantity can then be selected at will, and IMA can minimize the quantity  spread in the program map using full ballistic mode (see Fig. 7).

7

Injection-quantity program map of the piezo-inline injector

mm3 Lift

5

100 a b c

80   y    t    i    t   n   a   u   q    l   e   u    f      d   e    t   c   e    j   n    I

0

0.1

d

0.3

60

40 Fig. 7

e

20

0 0

0.4

0.8

1.2 ms

Triggering period

     E      4      8      9      1      K      M      U

     æ

Injected fuel quantities at different injection pressures a 1,600 bar b 1,200 bar c 1,000 bar d 800 bar e 250 bar

Function of the servo valve

a

b

c Fig. 6

1

a b

2 3

c

4

6

1

5 Rail pressure

Leakage-oil pressure

Control-chamber pressure

     E      5      8      9      1      K      M      U

     æ

2 3 4 5 6

Start position Nozzle needle opens (bypass closed, normal function with outlet and inlet restrictors) Nozzle needle closes (bypass open, function with two inlet restrictors) Ser vo valve (control valve) Outlet restrictor Control chamber Inlet restrictor No zzle needle Bypass

36

High-pressure components of common-rail system

Injector

Function of the hydraulic coupler  Another key component in the piezo-inline injector is the hydraulic coupler (Fig. 8, 3) that implements the following functions:  Translates and amplifies the actuator stroke.  Compensates for any play between the actuator and the servo valve (e.g. caused by thermal expansion).  Performs a failsafe function (automatic safety cutoff of fuel injection if electrical decontacting fails).

The actuator module and the hydraulic coupler are immersed in the diesel fuel flow at a pressure of about 10 bar. When the actuator is not triggered, pressure in the hydraulic coupler is in equilibrium with its surroundings. Changes in length caused by temperature are compensated by small leakage-fuel quantities via the guide clearances of the two plungers. This maintains the coupling of forces between actuator and switching valve at all times. 8

To generate an injection event, a voltage (110...150 V) is applied to the actuator until the equilibrium of forces between the switching valve and the actuator is exceeded. This increases the pressure in the coupler, and a small leakage volume flows out of the coupler via the piston guide clearances into the low-pressure circuit of the injector. The pressure drop caused in the coupler has no impact on injector function for a triggering period lasting several milliseconds. At the end of the injection process, the quantity missing in the hydraulic coupler needs refilling. This takes place in the reverse direction via the guide clearances of the plungers as a result of the pressure difference between the hydraulic coupler and the low-pressure circuit of the injector. The guide clearances and the low-pressure level are matched to fill up the hydraulic coupler fully before the next injection cycle starts.

Function of the hydraulic coupler

1 2

3

  e   g   a    t    l   o    V

  e   r   u   s   s   e   r   p   r   e    l   p   u   o    C

 pSystem

Recharging

Fig. 8

Rail pressure

1

Coupler pressure

2 3

Low-pressure fuel rail with valve Actuator Hydraulic coupler (translator)

10 bar 1 bar

  e   g   n   a    h  r   c  e    l   e   p   u   m   u  o    l   o  c   n    V    i

 pK <  pSystem

Leakage

 pK >  pSystem

Time t 

     E      6      8      9      1      K      M      U

     æ

High-pressure components of common-rail system

Injector

37

Benefits of the piezo-inline injector Triggering the common-rail piezo  Multiple injection with flexible start of inin-line injector  jection and intervals between individual The injector is triggered by an engine control unit whose output stage was specially deinjection events.  Production of very small injected fuel signed for these injectors. A reference triggering voltage is predetermined as a function of  quantities for pre-injection. the rail pressure of the set operating point.  Small size and low weight of injector The voltage signal is pulsed (Fig. 9) until (270 g compared to 490 g). there is a minimum deviation between the  Low noise (–3 dB [A]).  Lower fuel consumption (–3%). reference and the control voltage. The voltage rise is converted proportionally into a piezo Lower exhaust-gas emission (–20%).  Increased engine performance (+7%). electric actuator stroke. The actuator stroke produces a pressure rise in the coupler by  means of hydraulic translation until the equilibrium of forces is exceeded at the switching valve, and the valve 9 Triggering sequences of the piezo-inline injector for an injection event opens. As soon as the switching valve reaches its end position, pressure in the control a chamber starts to Voltage drop via the needle, and injection ends.

Current

b Valve lift

Coupler pressure

c

Injection rate

Needle lift Fig. 9

a

0.5

0.0

0.5 Time t 

1.0

1.5

ms

     E      7      8      9      1      K      M      U

     æ

b c

Current and voltage curves for triggering the injector Valve-lift curve and coupler pressure Valve-lift curve and injection rate

38

The piezoelectric effect



The piezoelectric effect

In 1880 Pierre Curie and his brother Jacques discovered a phenomenon that is still very little known today, but is present in the everyday lives of millions of people: the piezoelectric effect. For example, it keeps the pointers of a crystal clock operating in time.

Principle of the piezoelectric effect

(represented as a unit cell) a

Quartz crystal SiO2

b

Piezoelectric effect: When the crystal is compressed, negative O2– ions shift upward, positive Si4+ ions shift downward: Electric charges are induced at the crystal surface.

c

Inverse piezoelectric effect: By applying an electrical voltage, O2– ions shift upward, Si4+ ions shift downward: The crystal contracts.

Certain crystals (e.g.quartz and turmaline) are piezoelectric: Electric charges are induced on the crystal surface by exerting a compression or elongation force along certain crystal axes. This electrical polarization arises by shifting positive and negative ions in the crystal relative to each other by exerting force (see Fig., b). The shifted centers of charge gravity within the crystal compensate automatically, but an electric field forms between the end faces of the crystal. Compressing and elongating the crystal create inverse field directions. On the other hand, if an electrical voltage is applied to the end faces of the crystal, the effect reverses (inverse piezoelectric effect): The positive ions in the electric field migrate toward the negative electrode, and negative ions toward the positive electrode. The crystal then contracts or expands depending on the direction of the electric field strength (see Fig., c). The following applies to piezoelectric field strength E p: E p = δ ∆x/x  ∆x/x : relative compression or elongation piezoelectric coefficient, numeric value δ: 109 V/cm through 10 11 V/cm

a

The change in length ∆x  results from the following when a voltage U  is applied: U  / δ = ∆x  (using quartz as an example: deformation of about 10–9 cm at U  = 10 V) The piezoelectric effect is not only used in quartz clocks and piezo-inline injectors, it has many other industrial applications, either as a direct or inverse effect: Piezoelectric sensors are used for knock  control in gasoline engines. Forexample, they detect high-frequency engine vibrations as a feature of combustion knock. Converting mechanical vibration to electric voltage is also used in the crystal audio pickup of a record player or crystal microphones. The piezoelectric igniter (e.g.in a firelighter) causes mechanical pressure to produce the voltage to generate a spark. On the other hand, if an alternating voltage is applied to a piezoelectrical crystal, it vibrates mechanically at the same frequency as the alternating voltage. Oscillating crystals are used as stabilizers in electrical oscillating circuits or as piezoelectric acoustic sources to generate ultrasound. When used in clocks, the oscillating quartz is excited by an alternating voltage whose frequency is the same as the quartz’s natural frequency. This is how an extremely time-constant resonant frequency is generated. In a calibrated quartz, it deviates by only approx. 1/1,000 second per year.

b

c

+

4+

+

Si

2¯

O

 ¯ 

 ¯  +  ¯ 

 ¯ 

+

 ¯ 

¯ 

 ¯ 

¯ 

 ¯ 

¯ 

+

+

+

+

+

+

+

+  ¯  +

+

 ¯ 

 ¯   ¯ 

      Y       0       7       1       0       N       A       S

æ

Where does the word “electronics” come from?



Where does the word “electronics” come from?

This term actually goes back to the ancient Greeks. For them, the word “electron” meant amber. Its force of attraction on woollen threads or similar was known to Thales von Milet over 2,500 years ago. Electrons, and therefore electronics as such, are extremely fast due to their very small mass and electric charge. The term “electronics” comes directly from the word “electron”. The mass of an electron has as little effect on a gram of any given substance as a 5 gram weight has on the total mass of our earth. The word “electronics” was born in the 20th century. There is no evidence available as to when the word was used for the first time. It could be Sir John Ambrose Fleming, one of the inventors of the electron tube in about 1902.

Even the first “Electronic Engineer” already existed in the 19th century. Fleming was listed in the 1888 edition of “Who’s Who”, published during the reign of Queen Victoria. The official title was “Kelly’s Handbook of Titled, Landed and Official Classes”. The Electronic Engineer can be found under the title “Royal Warrant Holders”, that is the list of persons who had been awarded a Royal Warrant. What was this Electronic Engineer’s job? He was responsible for the correct functioning and cleanliness of the gas lamps at court. And why did he have such a splendid title? Because he knew that “electrons” in ancient Greece stood for glitter, shine, and sparkle. Source: “Basic Electronic Terms” (“Grundbegriffe der Elektronik”) – Bosch publication (reprint from the “Bosch Zünder” (Bosch C ompany Newspaper)), 1988.

      Y       7       4       0       0       E       A       L

     æ

39

40

High-pressure components of common-rail system

High-pressure pumps

High-pressure pumps Design and requirements The high-pressure pump is the interface between the low-pressure and high-pressure stages. Its function is to make make sure there is always sufficient fuel under pressure available in all engine operating conditions. conditions. At the same time it must operate for the entire service life life of the vehicle vehicle.. This include includess providing a fuel reserve that is required for quick engine starting and rapid pressure rise in the fuel rail. The high-pressure pump generates a constant system pressure for the high-pressure accumulator accum ulator (fuel rail) independent independent of fuel injection.. For this injection this reason, fuel – compared compared to to conventional fuel-injection systems – is not compressed during the injection process.

A 3-plunger radial-piston pump is used as the high-pressure pump to generate pressure in passenger-car passenger-car systems. 2-plunger in-line fuel-injection pumps are also used on commercial vehicles. Preferably Preferably,, the high-pressure pump is fitted to the diesel engine at the same point as a conv conventional entional distributor injection pump. pump. The pump is driven driven by the engine via coup coupling, ling, gearwhe gearwheel, el, chain chain,, or toothed belt. Pump speed is therefore coupled to engine speed via a fixed gear ratio.

1

Bosch high-pressure pumps for common-rail systems

Pump

Pressure in bar

Lubrication

CP 1

1,350

Fuel

CP1+

1,350

Fuel

CP1H CP1H-OHW

1,600 1,100

Fuel Fuel

CP3.2

1,600

Fuel

CP3.2+

1,600

Fuel

CP3.3

1,600

Fuel

CP3.4 CP3.4+

1,600 1,600

Oil Fuel

Table 1

CP2

1,400

Oil

H

CPN2.2

1,600

Oil

CPN2.2+

1,600

Oil

CPN2.4

1,600

Oil

Increa Incr ease sed d pr pres essu sure re section + Hi High gher er de delilive very ry ra rate te OHW Off-Highway

The pump plunger inside of the high-pressure pump compresses compresses the fuel. At three delivery strokes strokes per revolution, revolution, the radialpiston pump produces overlapping delivery  strokes (no interruption in delivery), delivery), low  drive peak torques, torques, and an even load on the pump drive. On passenger-car systems, torque reaches reaches 16 Nm, Nm, i.e. only 1/9t 1/9th h of the driv drivee torque torque required for a comparable distributor injection pump. pump. As a result, the common-rai common-raill system places fewer demands on the pumpdrive system than conv conventional entional fuel-injection systems. The power required to drive the pump increases in proportion to the pressure in the fuel rail and the rotational speed of the pump (delivery quantity). quantity). On a 2-liter 2-liter engine, the high-pressure pump draws a power power of 3.8 kW at nominal speed and a pressure of 1,350 bar in the the fuel rail (at a mechanical mechanical efficien efficiency cy of appr approx. ox. 90%). The higher power requirements of common-rail systems compared to conventional fuel-injection systems is caused by leakage and control volumes volumes in the injector, injector, and – on the high-pressure pump CP1 – the pressure drop to the required system pressure across the pressure-contr pressure-control ol valve. The high-pressure radial-piston pumps used in passenger cars are lubricated by fuel. Commercial-vehicle Commercial-v ehicle systems may have fuelor oil-lubricated oil-lubricated radial-piston pumps, as well as oil-lubricated 2-plunger in-line fuelinjection pumps. Oil-lubricated pumps are more robust against poor fuel quality. High-pressure pumps are used in a number of differ different ent designs designs in passenger cars and commercial vehicles. There are versions versions of  pump generations that have different delivery rates r ates and delivery pressures ( Table 1).

High-pressure components of common-rail system

Radial-piston pump (CP1 ( CP1)) Design The drive drive shaft in the housing housing of CP1 is mounted mount ed in a central central bearing (Fig. (Fig. 1, 1). The pump elements (3) are arranged radially with respect to the central bearing and offset by 120°. The eccenter eccenter (2) fitted to the drive shaft forces the pump plunger to move up and down.

Force is transmitted between the eccentric shaft and the delivery plunger by means of  a drive roller, roller, a sliding ring mounted on the shaft eccenter, eccenter, and a plunger base plate attached to the plunger base plate. Operating concept Fuel delivery and compression  The presupply pump – an electric fuel pump or a mechanically driven gear pump – delivers fuel via a filter and water separator to the inlet of the high-press high-pressure ure pump pump (6). The inlet is located located inside of the pump on passenpassenger-car systems with a gear pump flanged to the high-pressure pump. pump. A safety valve is is fit1

High-pressure pumps

41

ted behind behind the inlet. inlet. If the delive delivery ry pressure pressure of the presupply pump exceeds exceeds the opening opening pressure (0.5 to 1.5 bar) of the safety valve, the fuel is pressed through the restriction bore of the safety valve valve into the lubrication and cooling circuit of the high-pressure pump. The drive shaft with its its eccenter eccenter moves the pump plunger up and down to mimic the eccentric eccentric lift. Fuel passed through the high-pressure pump’s inlet valve (4) into the element chamber and the pump plunger moves downward (inlet stroke). When the bottom-dead center of the pump plunger is exceeded, exceeded, the inlet valve closes, and the fuel in the element chamber chamber can no longer escape. escape. It can then be pressurized beyond the delivery delivery pressure of the presupply pump. pump. The rising pressure opens opens the outlet valve (5) as soon as pressure reaches the level in the the fuel rail. The pressurized fuel then passes to the high-pressure high- pressure circuit.

High-pressure pump (schematic, cross-section)

4

5

3

2 1 6

Fig. 1

     Y      1         3      7      5      1      K      M      U

     æ

1 2 3 4 5 6

Drive sh shaft Eccenter Pump Pu mp el elem emen entt wi with th pump plunger Inlet valve Outlet valve Fuel inlet

42

High-pressure components of common-rail system

High-pressure pumps

The pump plunger continues to deliver fuel until it reaches its top-dead center position (delivery stroke). stroke). The pressure then drops drops so that the outlet outlet valve closes. The remaining fuel is depressurized and the pump plunger moves downward. When the pressure in the element chamber exceeds exceeds the pre-delivery pre-delivery pressure, the inlet valve reopens, and the process starts over. over. Transmission ratio The delivery delivery quantity quantity of a high-pressure high-pressure pump is proportional to its rotational speed. In turn, the pump speed is dependent on the engine engine speed. The transmission ratio between the engine and the pump is determined in the the process of adapting the fuelinjection system to the engine so as to limit the volume volume of exc excess ess fuel delivered delivered.. At the same time it makes sure that the engine’ engine’ss fuel demand at WOT is covered to the full extent. Possible gear ratios are 1:2 1:2 or 2:3 relative to the crankshaft.

2

Delivery rate As the high-pressure pump is designed for high delivery delivery quantities, there is a surplus of pressurized fuel when the engine is idling or running in part-load range. On firstgeneration systems with a CP1, excess fuel delivered is returned to the fuel tank by the pressure-controll valve on the fuel rail. As pressure-contro the compressed compressed fuel expands, the energy  imparted by compression is lost; overall efficiency drops. drops. Compressing and then expanding the fuel also heats the fuel.

High-pressure pump (CP1), (CP1), variant with mounted pressure-control valve (3D view)

1

2

3

4 5 6

7

Fig. 2

11 12 13 14 15 16 17

Flange Pump Pu mp hou housi sing ng Engine Eng ine cyl cylind inder er head head Inlet Inl et con connec nectio tion n High Hi gh-p -pres ressu sure re inlet inlet Return Ret urn con connec nectio tion n Pressu Pre ssurere-con contro troll valve 18 Ba Barr rrel el bo bolt lt 19 Sh Shaf aftt se seal al 10 Ecc Eccent entric ric sha shaft ft

10

9

8

     Y      2      2      0      2      K      M      U

     æ

High-pressure components of common-rail system

Radial-piston pump (CP1H) Modifications An improvement in energetic efficiency is possible by controlling fuel delivery by the high-pressure pump on the fuel-delivery  side (suction side). Fuel flowing into the pump element is metered by an infinitely  variable solenoid valve (metering unit, ZME). This valve adapts the fuel quantity  delivered to the rail to system demand. This fuel-delivery control not only drops the performance demand of the high-pressure pump, it also reduces the maximum fuel temperature. This system designed for the CP1H was taken over by the CP3. Compared to the high-pressure pump CP1, the CP1H is designed for higher pressures up to 1,600 bar. This was achieved by  reinforcing the drive mechanism, modifying the valve units, and introducing measures to increase the strength of the pump housing. The metering unit is mounted on the high-pressure pump (Fig. 3, 13).

High-pressure pumps

The solenoid valve is triggered by a PWM signal.

4

Metering unit design

1

2

Fig. 4

3

11 Plug with electrical interface 12 Magnet housing 13 Bearing 14 Armature with tappet 15 Winding with coil body 16 Cup 17 Residual air-gap washer 18 Magnetic core 19 O-ring 10 Plunger with control slots 11 Spring 12 Safety element

4 5 6

7 8 9 10

Design of the metering unit (ZME) Fig. 4 shows the design of the metering unit. The plunger operated by solenoid force frees up a metering orifice depending on its position. 3

43

9 11 12 9

     Y      6      1      0      2      K      M      U

     æ

High-pressure pump (CP1H) with metering unit (exploded view)

8

Fig. 3

9

11 12 13 14 15 16 17 18

10

7

11 12 6

13

19 14 15

1

2

3

4

5

     Y      5      1      0      2      K      M      U

     æ

10 11 12 13 14 15

Flange Eccentric shaft Bushing Drive roller Pump housing Plate Spring Engine cylinder head Return-flow connection Overflow valve Inlet connection Filter Metering unit Cage Pump plunger

44

High-pressure components of common-rail system

High-pressure pumps

Radial-piston pump (CP3) Modifications The CP3 is a high-pressure pump with suction-side fuel-delivery control by means of a metering unit (ZME). This control was first used on the CP3 and was assumed later on the CP1H. The principle design of the CP3 (Fig. 5) is similar to the CP1 and the CP1H. The main difference in features are:  Monobloc housing: This construction reduces the number of leak points in the high-pressure section, and permits a higher delivery rate.  Bucket tappets: Transverse forces arising from the transverse movement of the eccenter drive roller are not removed directly by the pump plungers but by buckets on the housing wall. The pump then has greater stability under load and is capable of withstanding higher pressures. Potentially, it can withstand pressures up to 1,800 bar. 5

Variants Pumps of the CP3 family are used in both passenger cars and commercial vehicles. A number of different variants are used depending on the delivery rate required. The size, and thus the delivery rate, increases from the CP3.2 to the CP3.4. The oil-lubricated CP3.4 is only used on heavy-duty  trucks. On light-duty trucks and vans, pumps primarily designed for passenger cars may also be used. A special feature of systems for mediumduty and heavy-duty trucks is the fuel filter located on the pressure side. It is situated between the gear pump and the high-pressure pump, and permits a greater filter storage capacity before requiring a change. The high-pressure pump requires an external connection for the fuel inlet in any case, even if the gear pump is flanged onto the high-pressure pump.

High-pressure pump CP3 with metering unit and mounted gear presupply pump

     Y      4      1      0      2      K      M      U

     æ

High-pressure components of common-rail system

In-line piston pump (CP2) Design The oil-lubricated, quantity-controlled high-pressure pump (CP2) is only used on commercial vehicles. This is a 2-plunger pump with an in-line design, i.e.the two pump plungers are arranged adjacently  (Fig. 6). A gear pump with a high gear ratio is located on the camshaft extension. Its function is to draw fuel from the fuel tank and route it to the fine filter. From there, the fuel passes through another line to the metering unit located on the upper section of the high-pressure pump. The metering unit controls the fuel quantity delivered for compression dependent on actual demand in the same way as other common-rail high-pressure pumps of the recent generation.

6

High-pressure pumps

45

Lube oil is supplied either directly via the mounting flange of the CP2 or a sidemounted inlet. The drive gear ratio is 1:2. The CP2 is therefore mountable together with conventional in-line fuel-injection pumps. Operating concept Fuel enters the pump element and the compressed fuel is conveyed to the fuel rail via a combined inlet/outlet valve on the CP2.

High-pressure pump CP2

6

1 7 2

Fig. 6

8

9 3

10 4 11

5 12

     Y      3      1      0      2      K      M      U

     æ

11 Zero delivery restrictor 12 Metering unit 13 Internal gear 14 Pinion 15 Gear presupply pump 16 High-pressure connection 17 Two-part inlet/outlet valve 18 C-coated plunger 19 Plunger return spring 10 Oil inlet 11 C-coated roller bolt 12 Concave cam

High-pressure components of common-rail system

46

Fuel rail (high-pressure accumulator)

Operating concept The pressurized fuel delivered by the highpressure pump passes via a high-pressure fuel line to the fuel-rail inlet (4). From there, it is distributed to the individual injectors (hence the term “common rail”).

Fuel rail (high-pressure accumulator) Function The function of the high-pressure accumulator (fuel rail) is to maintain the fuel at high pressure. In so doing, the accumulator volume has to dampen pressure fluctuations caused by fuel pulses delivered by the pump and the fuel-injection cycles. This ensures that, when the injector opens, the injection pressure remains constant. On the one hand, the accumulator volume must be large enough to meet this requirement. On the other hand, it must be small enough to ensure a fast enough pressure rise on engine start. Simulation calculations are conducted during the design phase to optimize the performance features. Besides acting as a fuel accumulator, the fuel rail also distributes fuel to the injectors.

The fuel pressure is measured by the railpressure sensor and controlled to the required value by the pressure-control valve. The pressure-relief valve is used as an alternative to the pressure-control valve – depending on system requirements – and its function is to limit fuel pressure in the fuel rail to the maximum permissible pressure. The highly compressed fuel is routed from the fuel rail to the injectors via high-pressure delivery lines. The cavity inside the fuel rail is permanently  filled with pressurized fuel. The compressibility of the fuel under high pressure is utilized to achieve an accumulator effect. When fuel is released from the fuel rail for injection, the pressure in the high-pressure accumulator remains virtually constant, even when large quantities of fuel are released.

Design The tube-shaped fuel rail (Fig. 1, 1) can have as many designs as there are engine mounting variants. It has mountings for the railpressure sensor (5) and a pressure-relief  valve or pressure-control valve (2).

1

Common rail with attached components

4 5 1

Fig. 1

1 2 3 4 5 6

Fuel rail Pressure-control valve Return line from fuel rail to fuel tank  Inlet from highpressure pump Rail-pressure sensor Fuel line to injector

2

3

6

     Y      6      9      9      1      K      M      S

     æ

High-pressure components of common-rail system

High-pressure sensors Application

In automotive applications, high-pressure sensors are used for measuring the pressures of fuels and brake fluids. Diesel rail-pressure sensor In the diesel engine, the rail-pressure sensor measures the pressure in the fuel rail of the common-rail accumulator-type injection system. Maximum operating (nominal) pressure  pmax is 160 MPa (1,600 bar). Fuel pressure is controlled by a closed control loop, and remains practically constant independent of load and engine speed. Any deviations from the setpoint pressure are compensated for by a pressure-control valve.

Design and operating concept

The heart of the sensor is a steel diaphragm onto which deformation resistors have been vapor-deposited in the form of a bridge circuit (Fig. 1, 3). The sensor’s pressuremeasuring range depends on diaphragm thickness (thicker diaphragms for higher

47

pressures and thinner ones for lower pressures). When the pressure is applied via the pressure connection (4) to one of the diaphragm faces, the resistances of the bridge resistors change due to diaphragm deformation (approx. 20 µm at 1,500 bar). The 0...80 mV output voltage generated by the bridge is conducted to an evaluation circuit which amplifies it to 0...5 V. This is used as the input to the ECU which refers to a stored characteristic curve in calculating the pressure (Fig. 2).

1

High-pressure sensor

2 cm 1

Gasoline rail-pressure sensor As its name implies, this sensor measures the pressure in the fuel rail of the DI Motronic with gasoline direct injection. Pressure is a function of load and engine speed and is 5...12 MPa (50...120 bar), and is used as an actual (measured) value in the closed-loop rail-pressure control. The rpm and loaddependent setpoint value is stored in a map and is adjusted at the rail by a pressure control valve. Brake-fluid pressure sensor Installed in the hydraulic modulator of  such driving-safety systems as ESP, this high-pressure sensor is used to measure the brake-fluid pressure which is usually  25 MPa (250 bar). Maximum pressure p max can climb to as much as 35 MPa (350 bar). Pressure measurement and monitoring is triggered by the ECU which also evaluates the return signals.

High-pressure sensors

2 3

Fig. 1 4

1

5

2 3

     Y      6      7      5      1      K      M      U

 p

     æ

2

High-pressure sensor (curve, example) V

4.5   e   g   a    t    l   o   v    t   u   p    t   u    O

0.5 0

 p max

Pressure

     E      2         9      1      7      0      E      A      U

     æ

4 5

Electrical connection (socket) Evaluation circuit Steel diaphragm with deformation resistors Pressure connection Mounting thread

48

High-pressure components of common-rail system

Pressure-control valve

Pressure-control valve Function

The function of the pressure-control valve is to adjust and maintain the pressure in the fuel rail as a factor of engine load, i.e.:  It opens when the rail pressure is too high. Part of the fuel then returns from the fuel rail via a common line to the fuel tank.  It closes when the rail pressure is too low, thus sealing the high-pressure side from the low-pressure side. Design

The pressure-control valve (Fig. 1) has a mounting flange which attaches it to the high-pressure pump or the fuel rail. The armature (5) forces a valve ball (6) against the valve seat in order to seal the high-pressure stage from the low-pressure stage; this is achieved by the combined action of a valve spring (2) and an electromagnet (4) which force the armature downwards. Fuel flows around the whole of the armature for lubrication and cooling purposes. Operating concept

The pressure-control valve has two closed control loops:  A slower, closed electrical control loop for setting a variable average pressure level in the fuel rail.  A faster hydromechanical control loop for balancing out high-frequency pressure pulses.

Pressure-control valve activated When the pressure in the high-pressure circuit needs to be increased, the force of the electromagnet is added to that of the spring. The pressure-control valve is activated and closes until a state of equilibrium is reached between the high pressure and the combined force of the electromagnet and the spring. At this point, it remains in partly open position and maintains a constant pressure. Variations in the delivery quantity of the high-pressure pump and the withdrawal of fuel from the fuel rail by the injectors are compensated by varying the valve aperture. The magnetic force of the electromagnet is proportional to the control current. The control current is varied by pulse-width modulation. A pulse frequency of 1 kHz is sufficiently high to prevent adverse armature movement or pressure fluctuations in the fuel rail. Designs

The pressure-control valve DRV1 is used in first-generation common-rail systems. Second- and third-generation CR systems operate using the two-actuator concept. Here, the rail pressure is adjusted by both a metering unit as well as a pressure-control valve. 1

Pressure-control valve DRV1 (section)

1

Fig. 1

11 Electrical connections 12 Valve spring 13 Armature 14 Valve housing 15 Solenoid coil 16 Valve ball 17 Support ring 18 O-ring 19 Filter 10 High-pressure fuel supply 11 Valve body 12 Drain to lowpressure circuit

Pressure-control valve not activated The high pressure present in the fuel rail or at the high-pressure pump outlet is applied to the pressure-control valve via the highpressure fuel supply. As the deengerized electromagnet exerts no force, the highpressure force is greater than the spring force. The pressure-control valve opens to a greater or lesser extent depending on the delivery quantity. The spring is dimensioned to maintain a pressure of approx. 100 bar.

2 3

4 5

12 11

6 7

10

8 9

     Y      7      0      0      2      K      M      U

     æ

High-pressure components of common-rail system

In this case, either the pressure-control valve DRV2 is used or the DRV3 variant for higher pressures. This control strategy  achieves lower fuel heating and eliminates the need for a fuel cooler. The DRV2/3 (Fig. 2) differs from the DRV1 in the following features:  Hard seal to the high-pressure interface (bite edge).  Optimized magnetic circuit (lower power consumption).  Flexible mounting concept (free plug orientation).

Pressure-control valve, pressure-relief valve

49

Pressure-relief valve Function

The pressure-relief valve has the same function as a pressure limiter. The latest version of the internal pressure-relief valve now has an integrated limp-home function. The pressure-relief valve limits pressure in the fuel rail by releasing a drain hole when pressure exceeds a certain limit. The limp-home function ensures that a certain pressure is maintained in the fuel rail to permit the vehicle to continue running without any  restriction. Design and operating concept

2

Pressure-control valve DRV2

1 2

3

4

5

6

7

8

The pressure-relief valve (Fig. 3) is a mechanical component. It consists of the following parts:  A housing with an external thread for screwing to the fuel rail.  A connection to the fuel-return line to the fuel tank (3).  A movable plunger (2).  A plunger return spring (5).

9

     Y      5      0      0      2      K      M      U

     æ

3

Pressure-relief valve DBV4

6

5

1

2

3

4

     Y      3      0      0      2      K      M      U

     æ

At the end which is screwed to the fuel rail, there is a hole in the valve housing which is sealed by the tapered end of the plunger resting against the valve seat inside the valve housing. At normal operating pressure, a spring presses the plunger against the valve seat so that the fuel rail remains sealed. Only if the pressure rises above the maximum system pressure is the plunger forced back against the action of the spring by the pressure in the fuel rail so that the highpressure fuel can escape. The fuel is routed through passages into a central bore of the plunger and returned to the fuel tank via a common line. As the valve opens, fuel can escape from the fuel rail to produce a reduction in fuel-rail pressure.

Fig. 2

1 2 3 4 5 6 7 8 9

Filter Bite edge Valve ball O-ring Union bolt with circlip Armature Solenoid co il Electrical connection Valve spring

Fig. 3

1 2 3 4 5 6

Valv e insert Valve plunger Low-pressure section Valv e holder Spring Diaphragm disc

50

Injection nozzles

Injection nozzles The injection nozzle injects the fuel into the combustion chamber of the diesel engine.It is a determining factor in the efficiency of mixture formation and combustion and, therefore has a fundamental effect on engine performance, exhaust-gas behavior, and noise. In order that injection nozzles can perform their function as effectively as possible, they have to  be designed to match the fuel-injection system and engine in which they are used. The injection nozzle is a central component of any fuel-injection system. It requires highly  specialized technical knowledge on the part of  its designers. The nozzle plays a major role in:  Shaping the rate-of-discharge curve (precise progression of pressure and fuel distribution relative to crankshaft rotation)  Optimum atomization and distribution of fuel in the combustion chamber, and  Sealing off the fuel-injection system from the combustion chamber Due to its exposed position in the combustion chamber, the nozzle is subjected to constant pulsating mechanical and thermal stresses from the engine and the fuel-injection system. The fuel flowing through the nozzle must also cool it. When the engine is overrunning, when no fuel is being injected, the nozzle temperature increases steeply. Therefore, it must have sufficient high-temperature resistance to cope with these conditions. In fuel-injection systems based on in-line injection pumps (Type PE) and distributor injection pumps (Type VE/VR), and in unit pump (UP) systems, the nozzle is combined with the nozzle holder to form the nozzleand-holder assembly (Fig. 1) and installed in the engine. In high-pressure fuel-injection systems, such as the Common R ail (CR) and unit injector (UI) systems the nozzle is a single integrated unit so that the nozzle holder is not required. Indirect-Injection (IDI)

engines use pintle nozzles, while direct-injection engines have hole-type nozzles.

The nozzles are opened by the fuel pressure. The nozzle opening, injection duration, and rate-of-discharge curve (injection pattern) are the essential determinants of injected fuel quantity. The nozzles must close rapidly and reliably when the fuel pressure drops. The closing pressure is at least 40 bar above the maximum combustion pressure in order to prevent unwanted post-injection or intrusion of combustion gases into the nozzle. The nozzle must be designed specifically for the type of engine in which it is used as determined by:  The injection method (direct or indirect)  The geometry of the combustion chamber  The required injection-jet shape and direction  The required penetration and atomization of the fuel jet  The required injection duration, and  The required injected fuel quantity  relative to crankshaft rotation Standardized dimensions and combinations provide the required degree of adaptability  combined with the minimum of component diversity. Due to the superior performance combined with lower fuel consumption that it offers, all new engine designs use direct in jection (and therefore hole-type nozzles). 1

The nozzle as the interface between fuel-injection system and diesel engine

PE

CR

VE/VR UP

UI Nozzle holder

Nozzle

Combustion chamber of diesel engine

      E      6      5      8      1       K       M       N

     æ

Injection nozzles



Dimensions of diesel fuel injection technology

Dimensions of diesel fuel-injection technology

The world of diesel fuel injection is a world of superlatives. The valve needle of a commercial-vehicle nozzle will open and close the nozzle more than a billion times in the course of its service life. It provides a reliable seal at pressures as high as 2,050 bar as well as having to withstand many other stresses such as:  The shocks caused by rapid opening and closing (on cars, this can take place as frequently as 10,000 times a minute if there are pre- and post-injection phases)  The high flow-related stresses during fuel injection, and  The pressure and temperature of the combustion chamber The facts and figures below illustrate what modern nozzles are capable of:  The pressure in the fuel-injection chamber can be as high as 2,050 bar. That is equivalent to the pressure produced by the weight of a large luxury sedan acting on an area the size of a fingernail.







The injection duration is 1...2 milliseconds (ms). In one millisecond, the sound wave from a loudspeaker only travels about 33 cm. The injection durations on a car engine vary between 1 mm3 (pre-injection) and 50 mm3 (full-load delivery); on a commercial vehicle, between 3 mm3 (pre-injection) and 350 mm3 (full-load delivery). 1 mm3 is equivalent to half the size of a pinhead. 350 mm3 is about the same as 12 large raindrops (30 mm3 per raindrop). That amount of fuel is forced at a velocity of 2,000 km/h through an opening of less than 0.25mm2 in the space of only 2 ms. The valve-needle clearance is 0.002 mm (2 µm). A human hair is 30 times thicker (0.06 mm).

Such high-precision technology demands an enormous amount of expertise in development, materials, production, and measurement techniques.

Human hair (dia. 0.06 mm) Pressure 2,050 bar Clearance 0.002 mm

Pinhead (2mm3)

Speed of sound 0.33 m/ms Injected fuel quantity 1... 350mm3

Injection duration 1...2 ms

      E      2         8      0      7      1       K       M       N

     æ

51

52

Injection nozzles

Hole-type nozzles

Design

Hole-type nozzles Application

Hole-type nozzles are used on engines that operate according to the Direct-Injection process (DI). The position in which the nozzles are fitted is generally determined by the engine design. The injection orifices are set at a variety of angles according to the requirements of the combustion chamber (Fig. 1). Hole-type nozzles are divided into:  Blind-hole nozzles  Sac-less (vco) nozzles Hole-type nozzles are also divided according to size into:  Type P which have a needle diameter of  4 mm (blind-hole and sac-less (vco) nozzles).  Type S which have a needle diameter of  5 or 6 mm (blind-hole nozzles for large engines). In Common-R ail (CR) and Unit Injector (UI) fuel-injection systems, the hole-type nozzle is a single integrated unit. It combines, therefore, the functions of the nozzle holder. The opening pressure of hole-type nozzles is in the range 150...350 bar. 1

Position of hole-type nozzle in combus tion chamber

γ 

1

2 3

Fig. 1

1 Nozzle holder or injector 2 Sealing washer 3 Hole-type nozzle

δ γ Inclination δ Jet cone angle

   Y    2      2    0    4    1    K    M    U

     æ

The injection orifices (Fig. 2, 6) are located on the sheath of the nozzle cone (7). The number and diameter are dependent on:  The required injected fuel quantity   The shape of the combustion chamber  The air vortex (whirl) inside of the combustion chamber The diameter of the injection orifices is slightly larger at the inner end than at the outer end. This difference is defined by the port taper factor. The leading edges of the injection orifices may be rounded by using the hydro-erosion (HE) process. This involves the use of an HE fluid that contains abrasive particles which smooth off the edges at points where high flow velocities occur (leading edges of injection orifices). Hydro-erosion can be used both on blindhole and sac-less (vco) nozzles. Its purpose is to:  optimize the flow-resistance coefficient  pre-empt erosion of edges caused by  particles in the fuel, and/or  tighten flow-rate tolerances Nozzles have to be carefully designed to match the engine in which they are used. Nozzle design plays a decisive role in the following:  Precise metering of injected fuel (injection duration and injected fuel quantity  relative to degrees of crankshaft rotation).  Fuel conditioning (number of jets, spray  shape and atomization of fuel).  Fuel dispersal inside the combustion chamber.  Sealing the fuel-injection system against the combustion chamber. The pressure chamber (10) is formed by  electrochemical machining (ECM). An electrode, through which an electrolyte solution is passed, is introduced into the pre-bored nozzle body. Material is then removed from the positively charged nozzle body (anodic dissolution).

Injection nozzles

Designs

Fuel in the volume below the nozzle-needle seat evaporates after combustion. This produces a large part of the engine's hydrocarbon emissions. For this reason, it is important to keep the dead volume, or “detrimental” volume, as small as possible. In addition, the geometry of the needle seat and the shape of the nozzle cone have a decisive influence on the opening and closing characteristics of the nozzle. This, in turn, affects the soot and NO x  emissions produced by the engine. The consideration of these various factors, in combination with the demands of  the engine and the fuel-injection system, has resulted in a variety of nozzle designs.

2

Hole-type nozzles

Blind-hole nozzle F F

1

14

2 13 12 11 F D

3

Fig. 2 10 9

  m   m    0    1

4

There are two basic designs:  Blind-hole nozzles  Sac-less (vco) nozzles

5

8

Among the blind-hole nozzles, there are a number of variants. Blind-hole nozzle The injection orifices in the blind-hole nozzle (Fig. 2, 6) are arranged around a blind hole. If the nozzle has a rounded tip , the injection orifices are drilled either mechanically  or by electro-erosion, depending on the design. In blind-hole nozzles with a conical tip , the injection orifices are generally created by  electro-erosion. Blind-hole nozzles may have a cylindrical or conical blind hole of varying dimensions. Blind-hole nozzles with a cylindrical blind  hole and rounded tip (Fig. 3), which consists of a cylindrical and a hemispherical section, offer a large amount of scope with regard to the number of holes, length of injection orifices, and spray-hole cone angle. The nozzle cone is hemispherical in shape, which – in combination with the shape of the blind hole – ensures that all the spray holes are of equal length.

53

6

7

   Y    4      3    0    4    1    K    M    S

     æ

3

11 Stroke-limiting shoulder 12 Fixing hole 13 Pressure shoulder 14 Secondary needle guide 15 Needle shaft 16 Injection orifice 17 Nozzle cone 18 Nozzle body 19 Nozzle-body shoulder 10 Pressure chamber 11 Inlet passage 12 Needle guide 13 Nozzle-body collar 14 Sealing face F F Spring force F D Force acting on

pressure shoulder due to fuel pressure

Features of a nozzle cone with cylindrical blind hole and rounded tip

Fig. 3

1 2 3

12 11 10

4 5

9

6

7

8

æ NMK1650-3Y

11 Shoulder 12 Seat lead-in 13 Needle-seat face 14 Needle tip 15 Injection orifice 16 Rounded tip 17 Cylindrical blind hole (dead volume) 18 Injection orifice leading edge 19 Neck radius 10 Nozzle-cone taper 11 Nozzle-body seat face 12 Damping taper

54

Injection nozzles

Hole-type nozzles

The blind-hole nozzle with a cylindrical blind  hole and conical tip (Fig. 4a) is only available for spray-hole lengths of 0.6 mm. The conical tip shape increases tip strength as a result of a greater wall thickness between the neck  radius (3) and the nozzle body seat (4). 4

Nozzle cones

A further refinement of the blind-hole nozzle  is the micro-blind-hole nozzle (Fig. 4c). Its blind-hole volume is around 30% smaller than that of a conventional blind-hole nozzle. This type of nozzle is particularly suited to use in common-rail systems, which operate with a relatively slow needle lift and, consequently, a comparatively long nozzleseat restriction. The micro-blind-hole nozzle currently represents the best compromise between minimizing dead volume and even spray dispersal when the nozzle opens for common-rail systems.

a

4 1

3

2

b

Sac-less (vco) nozzles In order to minimize dead volume – and therefore HC emissions – the injection orifice exits from the nozzle-body seat face. When the nozzle is closed, the nozzle needle more or less covers the injection orifice so that there is no direct connection between the blind hole and the combustion chamber (Fig. 4d). The blind-hole volume is considerably smaller than that of a blind-hole nozzle. Sac-less (vco) nozzles have a significantly  lower stress capacity than blind-hole nozzles and can therefore only be produced with a spray-hole length of 1 mm. The nozzle tip has a conical shape. The injection orifices are generally produced by electro-erosion.

5 2

c 

Fig. 4

a Cylindrical blind hole and conical tip a Conical blind hole and conical tip c Micro-blind-hole d Sac-less (vco) nozzle 1 2 3 4

Cylindrical blind hole Conical tip Neck radius Nozzle-body seat face 5 Conical blind hole

Blind-hole nozzles with conical blind holes  and conical tip (Fig. 4b) have a smaller dead volume than nozzles with a cylindrical blind hole. The volume of the blind hole is between that of a sac-less (vco) nozzle and a blind-hole nozzle with a cylindrical blind hole. In order to obtain an even wall thickness throughout the tip, it is shaped conically to match the shape of the blind hole.

d

   Y    8    5    8    1    K    M    N

     æ

Special spray-hole geometries, secondary  needle guides, and complex needle-tip geometries are used to further improve spray dispersal, and consequently mixture formation, on both blind-hole and sac-less (vco) nozzles.

Injection nozzles

Heat shield

The maximum temperature capacity of  hole-type nozzles is around 300°C (heat resistance of material). Thermal-protection sleeves are available for operation in especially difficult conditions, and there are even cooled nozzles for large-scale engines.

Hole-type nozzles

55

in the production of large amounts of soot. Hole-type nozzles have up to six injection orifices in passenger cars and up to ten in commercial vehicles. The aim of future development will be to further increase the number of injection orifices and to reduce their bore size (